Preliminary Report on the Lead and Zinc Deposits of Southwestern Wisconsin

Front matter

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Chapter II. Physical Features 9-20 Topography 9

The mounds 9

The uplands 10

The valleys 10

The peneplain 11

Amount of erosion ' 12

The drif tless area 12

Soils 14

Composition of the soils 14

Thickness of the soils 16

Amount of rock represented by the soils 17

Amount of erosion 18

Loess and alluvium 19

Drainage 19

Chapter III. General Geology 21-38 Potsdam sandstone 23

Lower magnesian limestone 23

St. Peter sandstone 24

Unusual section at the top of the St. Peter 24 iT CONTENTS.

Chapter III. General Geology — continued. p^Q"

Trenton limestone 25

The buff limestone 25

The glass rock 26

Gralena limestone 27

Separation between the Trenton and the Galena 28

I. Section at the Graham mine 29

II. Section at the Phillips and Bice mine 29

III. Section at the Tippecanoe mine 30

rV. Section at a quarry west of Platteville 30

V. Section at the Enterprise mine 31

VI. Section at the Gritty Six mine 31

VII. Section at the Kennedy mine near Hazel Green 31

VIII. Section at Mineral Point 31

IX. Section at the Penitentiary mine 32

X. Section at the Ellsworth mine 32

XI. Section at the Glanville mine 32

XII. Section at the Kennedy mine at Highland 33

XIII. Section at the Little Giant mine 33

XIV. Section at Darlington 34

The oil rock 34

General section and r^sum^ 35

Hudson River shales 36

Niagara limestone 37

Later formations 37

Chapter IV. The Ores and Associated Minerals 39-44 The ores 39

Lead ores 39

Galenite 39

Cerussite 40

Anglesite 40

Zinc ores 40

Sphalerite 40

Smithsonite 41

Hydrozincite 41

Calamine 41

Other ores 41

Iron ores 41

Copper ores 43

Manganese ores " 43

Contents

Chapter IV. The Ores and Associated Minerals— continued. p^g"

Associated minerals 43

Calcite 43

Dolomite 43

Selenite 43

Barite 44

Quartz 44

Sulphur 44

Chapter V. Outline of the Genesis of Ore Deposits 45-58 Zones of the earth's crust 45

The general circulation of water 47

Openings in rocks 48

The flowage of underground water 50

The work of underground water 54

Solution 54

Transportation 56

DejKJsition 56

Deposits made by ascending and by descending solutions 7

Chapter VI. The Ore Deposits 59-90 Rocks in which the ores occur 60

Form of the deposits 60

Crevice deposits 61

Order of deposition of the ores 63

Honeycomb deposits 64

Disseminated deposits 64

Description of mines 67

Enterprise mine at Platteville 67

New Deal and Kennedy mines near Hazel Green 69

Trego, Raisbeck an d Gritty Six mines near Meeker's Grove 71

Little Giant mine near Shullsburg 72

Oldenberg mine near Galena 73

Strawberry Blonde mine at Strawbridge 73

G raham mine near Platteville 74

Secondary ores 74

Origin of the ores 77

Localization of the ore deposits 87 vi CONTENTS,

PAGB

Chapter VII. General Considerations 91-87 Mining 91

Concentrating 92

Other mineral resources 93

Future geological work 91

Conclusions 96

ILLUSTRATIONS.

Plate. Facing Page.

I. Sketch map of the Upper Mississippi Valley lead and zinc district 1

II. Geological map of Grant, Lafayette and Iowa counties, Wisconsin 21

III. Fig. 1. Joint faces in Trenton limestone 25

Fig. 2. Contact of St. Peter sandstone and Trenton limestone 25

IV. Fig. 1. Disseminated ore in the blue limestone 65

Fig. 2. Cross section of stalactite-like mass of sphalerite 65

Fig. 3. Disseminated ore in oil rock 65

Fig. 4. Blue limestone with barite, sphalerite and galena. .. 65

Figure. Page.

1. Horizontal flow of water between two wells 50

2. Vertical flow of water between two wells 51

3. Underground flowage of water 52

4. Underground flowage of water in large openings 53

5. Fats and pitches 62

6. Map of Enterprise mine at Platteville 68

7. Deposition and alteration of ores 75

8. Generalized section across lead and zinc district 81

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THE LEAD AND ZINC DEPOSITS OF SOUTfi- WESTEKN WISCONSIN. ' <

Introduction

HISTORICATi.

The lead and zinc mines of the Mississippi valley may be grouped into three divisions:^ (1) Those of the Ozark region; (2) those of the Upper Mississippi valley; and (3) those of outlying districts including (a) southern Arkansas and (b) an area in Kentucky and southern Illinois. The Upper Mississippi valley district comprises: (1) Grant, Lafayette and Iowa counties, Wisconsin: (2) Jo Daviess couaty, Illinois; and (3) Dubuque county, Iowa. From certain other couaties adjoining these five, small amounts of ore have been produced, and the niain production has coane from: the three Wisconsin counties mentioned. The lead and zinc deposits of these Wisconsin counties form the subject of this report.*

In the Upper Mississippi valley, lead seem» to have been discovered by Nicholas Perrott about 1692.* This metal was also noted by Le Sueur in 1700 or 1701, and by John Carver in 1766. The first mining in the district was done on the

iC. R. Van Hise and H. F. Bain: "Lead- and zinc-deposits of the Mississippi valley, U. S. A.," Trans. Inst. Mining Engineers (England), vol. xxiii, p. 378, 1902.

2 See plate I.

8 Arthur Winslow: "Lead and zinc deposits," Mo. Geol. Survey, vol. vi, p. 145, 1894.

2 I^B^'AND zinc deposits of WISCONSIN.

site o:f«jliQ'prese(nt city of Dubuque in 1788 by Julien Dubuque, who'^Wdined from tlie Indians land on which, lead had been ^iscovBred a few years previously. After Dubuque's death in \^ 1810, little was done until after 1820, and before 1830 min- •* >-jng had become quite general in the vicinity of Dubuque and ■•/ Galena, and also in southwestern Wisconsin. From this timie down to the present day mining has been carried on continuously in the Upper Mississippi valley district, with certain periods in which the district figured prominently as a producer of lead and zinc.

The early work, and in fact that for years afterw^ard, was devoted entirely to the mining of lead, the zinc ores being unrecognized or, when recognized, regarded as of little value. It was not until some forty years ago that zinc ores were mined in this region, and the amount of these ores produced rapidly increased until the district became more important as a source of zinc than of lead. Of late years, due to a nimaber of causes, the activity of the district has decreased, but the last two years, — especially 1902, — ^have seen a marked revival in mining interest, — a revival which promises well to continue.

The ores mined are galena or "mineral" (sulphide of lead), smithsonite or "dry-bone" (carbonate of zinc), and sphalerite or "black jack" (sulphide of zinc). In relative am:ount of production sphalerite is the most important, smithsonite of less importance, and galena less still. The future will undoubtedly witness a continued increase in the importance of sphalerite.

PKEVTOUS REPORTS AND MAPS.

In addition to some earlier reports by Daniels, Percival and Whitney,^ the former Geological Survey of Wisconsin issued two important papers dealing with the lead and zinc deposits. The eajlier of these was by Moses Strong,^ and the latter by

^A list of these reports wiU be found on a later page. 2i"Geology and topography of the lead region," Geol. of Wis., vol. ii, pp. 643-752, 1877.

INTRODUCTION. 3

tlie*Cliief Geologist, T. O. Ohamberlin/ The Survey also issued an atlas of maps, included in which axe a numiber relating directly to the lead and zinc region. These are (1) geological maps of the counties, (2) geological and tx>pographical maps, scale about one inch to one mile, of the important oreproducing districts, and (3) large scale crevice mjaps of the different districts. The latter show in detail a laxge number of the crevices from which lead, or lead and zinc, ores have been obtained.^

Recently C. IL Van Hise^ has discussed the principles of ore deposition and has noted particular applications of these principles to the Upper Mississippi Valley lead and zinc district, and H. F. Bain* has presented a report on the lead and zinc deposits of the Ozark region.

The report by Chamberlin, just cited, is a very complete and exhaustive account of the district under consideration, — ^by f ar the best account written. The paper by Van Hise presents in a masterly way the modern theory and principles of ore deposition and the application of the same to the Wisconsin district, while the paper by Bain discusses, in the light of these principles, the closely related lead and zinc deposits of Missouri. To these three papei's the writer is especially indebted, — in fact the indebtedness is so great that it is practically impossible to refer to the proper source each of the statements miade in this report of facts which have already been stated by others. For

i"The ore deposits of southwestern Wisconsin," Ibid., vol. iv, pp. 365-571, 1882.

2 The reports and atlas of the former Geological Survey are unfortunately out of print, but they can be obtained at times from dealers in second-hand books. The atlas plates of importance in the lead and zinc district are: V to IX (sometimes numbered III to VII )» XIII, XVI, XXXI to XL.

8 "Some principles controlling the deposition of ores," Trans. Amer. Inst. Mining Eng., vol. xxx, pp. 27-177, 1901.

4 "Preliminary report on the lead and zinc deposits of the Ozark region, with an introduction by C. R. Van Hise, and chapters on the physiography and geology by G. I. Adams," 22nd Ann. Rept. U. S. Geol. Survey, pt. ii, pp. 23-227, 1902.

4 imAD AND ZINC DEPOSITS OF WISCONSIN.

this reafion this general acknowledgmeat is here made, not only to tbese papers just mentioned, but also to others treating of this region. It seldom happens that a preliminary report like the present has to deal with a district which has been so carefully studied by others; and were it not for. this previous work on the district it would have been impossible in the brief period available for the preparation of this report to have presented anything but an account of certain limited parts of the district. Three of the sheets of the Topographic Atlas of the United States, published by the United States Geological Survey, include a large part of the territory in the Wisconsin lead and zinc district. These are the Elkader, Lancaster and Mineral Point sheets ; the scale of these is one-half inch to the mile and the contour interval is twenty feet.^

Bibliography.

Below will be foimd a partial list of the papers dealing with Hie Upper Mississippi Valley lead and zinc district This list does not contain papers which treat solely of the paleontology and the Pleistocene geology.

J. T. Hodge: "On the Wisconsin and Missouri lead region," Amer. Jour. Sci., ser. i, vol. xliii, pp. 35-72.

Edwakd Daniels: "Some features of the lead district of Wisconsin,"

Proc. Boston Soc. Nat. Hist, vol. v, pp. 387-389. Edward Daniels: First Ann. Rept. Geol. Survey of Wis., pp. 7-66. J. D. Whitney: "Metallic wealth of the United States," pp. 403-417.

1855 J. G. Peecival: Ann. Rept. Geol. Survey of Wis., pp. 7-101.

1858 J. D. Whitney: Geol. of Iowa, vol. i, pt. 1, pp. 422-471.

1 These sheets may be obtained from the Director of the U. S. Geological Survey, Washington, D. C. The price is five cents each.

INTRODUCTION. 5

J. D. Whitney: "Report on the lead region of Wisconsin," Geol. Survey of Wis., vol. 1, pp. 73-420.

J. D. Whitney: "Geology of the lead region," Geol. Survey of 111., vol. 1, pp. 153-207. Also In Economical Geol. of 111., vol. i, pp. 188-162, 1882.

C. A. White: "Lead and zinc," Geol. Survey of Iowa, vol. ii, pp. 339-342.

James Shaw: "Geology of northwestern Illinois," Geol. Survey of

111., vol. V, pp. 1-24. Also in £2conomical Geol. of 111., vol. iii, pp.

1-20, 1882.

James Shaw: "Geology of Jo Daviess county," Geol. Survey of 111.,

vol. V, pp. 25-66. Also In Economical Geol. of 111., vol. Iii, pp.

20-54, 1882.

Moses Strong: "Geology and topography of the lead region," Geol. of Wis., vol. ii, pp. 643-752.

T. C. Chambeblin: "The ore deposits of southwestern Wisconsin,** Geol. of Wis., vol. iv, pp. 365-571.

1883 MosES Strong: "Lead and zinc ores," Geol. of Wis., vol. i, pp. 637-655.

W. P. Blake: "The progress of geological surveys in the state of Wisconsin — a review and bibliography," Trans. Wis. Acad. Sci., Arts and Letters, vol. ix, pp. 225-231.

Abthxtb Winslow: "Notes on the lead and zinc deposits of the Mississippi valley and the origin of the ores," Jour, of Geol., vol. 1, pp. 612-619.

W. P. Blake: "Wisconsin lead and zinc deposits," Bull. Geol. Soc. of Amer., vol. v, pp. 25-32.

6 miAD AND ZINC DEPOSITS OF WISCONSIN.

W. P. Blake: "The mineral deposits of southwestern Wijconsin," Trans. Amer. Inst Mining Eng., vol. xxii, pp. 558-568. Also in Amer. Geol., vol. xii, pp. 2'37-248.

W. P. Blake: "Discussion on lead and zinc deposits of the Mississippi valley," Trans. Amer. Inst. Mining Eng., vol. xxii, pp. 621- 634.

W. P. Blake: "Discussion on genesis of ore deposits," Trans. Amer. Inst Mining Eng., vol. xxiii, p. 587.

T. C. Chambeblin: "Discussion on Wisconsin lead and zinc deposits," Bull. Geol. Soc. Amer., vol. v, p. 32.

W. P. Jenney: "Lead and zinc deposits of the Mississippi valley," Trans. Amer. Inst. Mining Eng., vol. xxii, pp. 171-225, 642-646; especially pp. 208-212.

A. G. Leonabd: "Occurrence of zinc in northeastern Iowa," Proc Iowa Acad. Sci., vol. i, pt. iv, pp. 48-52.

Abthub Winslow: "Lead and zinc deposits," Mo. Geol. Survey, vol. vi and vii; especially vol. vi, pp. 135-149.

Abthub Winslow: "Discussion on lead and zinc deposits of the Mississippi valley," Trans. Amer. Inst. Mining Eng., vol. xxii, pp. 634-636.

W. H. HoBBs: "A contribution to the mineralogy of Wisconsin," Bull.

Univ. of Wis., sci. ser., vol. i, pp. 109-156. Also in Zeitsch. f. Kryst.,

vol. XXV, pp. 257-275.

A. G. Leonabd: "Origin of the Iowa lead and zinc deposits," Amer.

A. G. Leonabd: "Lansing lead mines," Proc. Iowa Acad. Sci., vol. il,

A. G. Leonabd: "Lead and zinc deposits of Iowa," Eng. and Mining

Jour., vol. Ixi, p. 614.

A. G. Leonabd: "Lead and zinc. A description of the mines of Iowa

in the Upper Mississippi region," Colliery Eng., vol. xvii, pp.

121-122.

A. G. Leonabd: "Lead and zinc deposits of Iowa," Iowa Geol. Survey, vol. vi, pp. 9-66.

Samuel Calvin and H. F. Bain: "Geology of Dubuque county," Iowa vol. X, pp. 379-622; especially pp. 480-597.

INTRODUCTION. 7

G. D. Hubbabd: "The Blue Mound quartzlte," Amer. Geol., vol. xxvi, pp. 163-168.

S. H. Ball and A. F. Smith: "The geology and ore deposition of the

Benton district, Lafayette county, Wisconsin/' Thesis, Univ. of

Wis. Not published, but in University library. C. R. Van Hise: "Some principles controlling the deposition of ores/*

Trans. Amer. Inst. Mining Eng., vol. xxx, pp. 27-177; especially

H. F. Bain: "Preliminary report on the lead and zinc deposits of the Ozark region, with an introduction by C. R. Van Hise, and chapters on the physiography and geology by G. I. Adams,'' 22nd Ann. Rept U. S. Gleol. Survey, pt. ii, pp. 23-227.

C. R. Van Hise and H. F. Bain: "Lead- and zinc-deposits of the Mississippi valley, U. S. A.," Trans. Inst Mining Engineers (England), vol. xxiii, pp. 376-434; especially pp. 409-420.

OBJECT AND SCQPE OF THIS BEPOBT.

In the preparation of this report three objects have been kept in mind : (1) To attempt to bring the knowledge of the geology, more especially the geology of the ore deposits, of the district down to the present time, — ^no complete discussion of the district has been published since the report by Chamberlin^ twenty years ago, — and to present such additional information as may have been obtained in the progress of the work. (2) To present an account of the district in a somewhat brief report which would be of use to those interested in the district and to the public in generaL (3) To give a careful and as accurate a statenuent as possible concerning the present and future outlook for mining in the district. How far the writer has succeeded in acoamplishing these ends is for others than himjself to judge. He recognizes, probably miore keenly than anyone else, the difficulties in making a brief report on a district which has been so

i'*Tlie ore deposits of southwestern Wisconsin," Geol. of Wis., vol. Iv, pp. 365-571, 1882.

much worked over by others and concerning which such different views have been held.

This account makes no pretense to completeness. The time available for the field work and for the preparation of the report was too brief to allow of anything more than a preliminary reports

ACKNO WLEDQMEN TS.

The writer's indebtedness to previous reports on this district has already been noted.^

To the Director of the Survey, Professor E. A. Birge, and to the consulting Geologist, Professor C. K. Van Hise, thaaks are due for miaay kindnesses. The work was carried on under the general supervision of the latter, and the ajssistance and helpful suggestions derived from him were a very imjportant aid. Thanks are due to Dr. H. Foster Bain for kindly criticisms. In part of the field work Mr. E. E. Ellis of Northwestern University, acted as assistant

The people of the district have been uniformjly kind and genei'ous in their interest in the work and in furnishing freely such informiation as it was possible to give. A list of those to whom thanks are due would include nearly all the mine owners, managers and superintendents in the district, as well as a number of individuals who are not directly interested in mining.

PHYSICAL FEATURES.

CHAPTER IL

PHYSICAL FEATURES.

TOPOGIIAPHY.

The surface of this district (including Grant^ Lafayette and Iowa counties) is fairly uniform in its general features throu^- out these three counties, with the exception of the immediate valley of the Wisconsin on the north and that of the Mississippi on the west Away from the vicinily of these two large valleys the topographic features may be grouped under three heads: (1) the mounds, (2) the uplands, and (3) the valleys.

The mounds.

The important mounds are the Blue, Platte and Sinsinawa. These are roughly circular elevations of small extent, usually with flat tops, which rise some 200 feet above the surrounding country. These mounds closely resemble others of the same character which are found to the east of the lead and zinc district in Wisconsin, and also to the south in Illinois. In general the mounds are capped by Niagara limestone, which has acted as a protection to the underlying softer Hudson Eiver shales. This limestone frequently contains large amounts of flints, and at the west of the Blue mounds the upper rock layer is of a flinty or quartzite-like nature.^ These caps of Niagara limjestone are

1 Moses Strong: ''Geology and topography of the lead region/' GeoL of Wis., vol. 11, p. 661, 1877.

G. D. Hubbard: "The Blue Mound quartzite," Amer. Geol., vol. xxvl, pp. 163-168, 1900.

all tliat is now left of a layer of this formation which, has been remioved by erosion from over a large part, if not from the whole, of the district

The uplands.

The uplands consist of rather level-topped elevations or ridges which separate the valleys. In fact the whole upland surface may be conBidered as a gently undulating plain which slopes gradually to the southwest. Above the plain rise the scattered msounds and in it have been cut the numierous valleys. The general features of this plain may be seen froim almost any of the larger stream divides of the region! A very good view of the topographic features of the district can be had from the Chicago and Northwestern railroad which traverses the plain from Blue Mounds to Fennimore along what is known as the Military ridge ; also along the Lancaster branch of this railroad and along the Galena branch north of Cuba City.

The valleys.

Each valley, as one descends it, is seen to consist first of a sag with gently sloping convex sides which merge gradually into the general surface of the upland plain. Lower down the valley floor has a steeper slope and the sides are steeper also, but still of gradual slope. Farther down still the narrow valley widens out, has a less marked slope and acquires a rather wide flat bottom. These flatrbottom|ed valleys are characteristic of all the larger streams and of miany of the smaller ones also. At timles the calley is bounded by steep slopes or cliffs, and these cliffs are commonly of Trenton limestone. Sometimes they are of Galena limestone, and much less commonly of St. Peter sandstone. A good example of these sandstone cliffs nuay be seen just west of Mineral Point, where the St Peter is more consolidated than usual. The bottoms of the valleys are from 100 to 400 feet, in places more, below the general level of the district, and continuous slopes of 200 feet in altitude are common along the valley sides.

PHYSICAL FEATURES. H

The peneplain.

The present topography of the district is due to sub-aerial erosion acting on approximately horizontal strata. The general history of the erosion may be summied up as follows: After the deposition of the Niagara limestone there is no absolute proof that other and later formations were deposited. If such were deposited they have been entirely removed by erosion, and of such earlier erosion we have no certain records. There is, however, one period of erosion which has left marked records^ and this is the period in which the land stood in a uniform position long enough for streams to reduce the whole district to a nearly level region or peneplain. This peneplain is now represented by tlie level uplands already described. The only parts of the district which were not reduced to the general level are the mounds, which rise as monadnocks above the peneplain. The date of the formation of this peneplain is not certainly known, but it may be of Tertiary age, and if so is thus later than the possibly Cretaceous peneplain which is exhibited farther north in central Wisconsin.^ After the formation of this peneplain the land was elevated, and erosion again began its work cutting into the surface and forming the present valleys. This elevation took place before Glacial time, and there is some evidence to show that at one time during this period of erosion the land stood at a somewhat higher altitude than, at present Since the revival of erosion a large portion of the district has been lowered, and the region is now in a stage where the streams are not so rapidly deepening their valleys as the valleys are widening. The district has passed through the stage of most marked relief and has entered on the stage where future erosion will tend to subdue rather than to accentuate the present differences of topography. The district may thus be said to be interniediate between maturity and old age, although much nearer the former than the latter.

iC. R, Van Hise: "A central Wisconsin baselevel," Science, new ser., vol. Iv, pp. 57-59, 1896. "A northern Michigan baselevel," Ibid., pp. 217-220.

Amount of erosion.

As an approximiate estimate of material which has been ^e^- moved froani the district since the formation of the peneplain and the subsequent reelevation of the land it may be said that the bulk of the hills, or the uplands between the streams, equals approximately the cubic contents of the valleys.^ In other words, if the district were to be leveled off the resulting surface would be about half way between the bottoms of the main valleys and the uplands (not the hills formed by the mounds). If the miain valleys average 300 to 400 feet below the peneplain surface, we have a sheet of material, 150 to 200 feet in thickness and extending over the whole district, which has been removed by erosion since the elevation of the land subsequent to the formation of the peneplain. This period of elevation dates late in geological time, although antedating the Glacial period. That erosion may have removed a greater thickness than this is probable from a consideration of the soils. ^

THE DBIFTLESS ABEA.^

Covering the northern states is a layer of unconsolidated material known as the glacial drift, or simply as the drift. This varies in thickness from nothing up to a few hundred feet and is composed of sometimes stratified and sometinDes unstratified mixtures of clay, rock-flour, sand, gravel and boulders of various sizes. Beneath the drift the solid rock is commonly scratched, smoothed or polished, and there is a sharp line of demarcation between this rock and the overlying material. The surface of the drift is now rough and hilly, now undulating, and now smooth. There is a lack of system in the arrangem!ent of the topographic features and the streams, which wander about often apparently aimlessly. Moreover, none but the larger streams

1 See page 18.

2T. C. ChamberUn and R. D. Salisbury: "Preliminary pcper on the drlftlesB area of the Upper Mississippi valley/' 6th Ann. Rept U. S. G«>I. Survey, p. 257, 1885.

8 For a detailed account of the drlftless area consult the paper by T. C. Chamberlin and R. D. Salisbury Just cited. The area is enclosed fine on plate I.

have well defined valleys, and there are numerous swampa and lakes. The district is topographically young, — very young, at least away from the southern edge of the drift. These features are due to a great continental glacier which camie from the north and extended as far south as the Ohio and Missouri rivers.

Lying well north of the southern limit of, and completely surrounded by, tliis drift-covered area is a district which has no drift and which possesses features markedly different from those just mentioned. This is known as the driftless area/ There is no drift here ; the underlying rock is not scratched or sm^oothed and it is not sharply marked off from the unconsolidated material above ; the topographic features are systemiatized, and even the smaller streams have well defined valleys and comparatively straight courses; there are no swamps, except along river bottoms, and no lakes ; the district is topographically mature. This driftless area, comprising some 10,000 square miles in the Upper Mississippi valley, lies m>ostly in southwestern Wisconsin but enters adjacent portions of Minnesota, Iowa and Illinois. Grant, Lafayette and Iowa counties, Wisconsin, lie wholly within the driftless area.

The reason, or reasons, why this district, which is not of higher altitude than the surrounding region, — even lower than much of it, — escaped glaciation while the surrounding country was covered by ice, has been a subject for speculation and investigation. It is generally conceded that the lack of glaciation is chiefly due to the fact that the ice, coming from the north and northeast, had its main currents deflected by the large valleys of lake Superior and lake Michigan and by the high lands in Wisconsin to the north and northeast of the driftless area. The possibility of local glacial deposits in this district has been noted, ^ and the fact that the district was never covered by mov-

iSee plate I.

2G. H. Squier: "Studies in the driftless area of Wisconsin/' Jour, of Geol., vol. v, pp. 825-836, 1897. Ibid., vol. vi, pp. 182-192, 1898. Ibid., vol. vii, pp. 79-82, 1899.

F. W. Sardeson: "On glacial deposits in tbe driftless area," Amer. Geol., vol. XX, pp. 392-403, 1897.

ing ice, while the entire surrounding country was thus deeply covered, is one of the most peculiar and striking phenomena in the whole range of glacial history.

SOILS.

Unlike the soils of the northern states in general, which are coanposed of material which has no imanediate relationship to the underlying rock, the soils of the drif tless area have the most intimate connection with subjacent rock. In fact these soils are derived by a process of decay from the country rock, and for this reason the character of the soil in any particular part of the driftless area is conditioned by the character of the underlying rock. The soil in a limestone area will thus differ widely from the soil of an area underlain by sandstone. In the latter the soil is composed largely of silica, in the fomer the soil does not closely resemble the original limestone but is m)ainly clay derived from this limestone. In other words, the limestone soils do not have the composition of the original rock, but are made up of the non-essential constitutentfi, or what might be termed the impurities, of that rock.

Composition of the soils.

The mlain limestone of the district, — the Galena, — consists essentially of a mixture of calcium carbonate and magnesium: carbonate, together Avith certain impurities. These impurities are chiefly three substances: (1) quartz, (2) oxide (and probably carbonate) of iron, (3) clay. When the limestone is exposed to the agents of weathering the two carbonates just mantioned are dissolved and carried away by percolating waters, while the impurities of the rock in general renmin. The chemical composition and the relative percentages of the components of the rock and those of the soils thus differ materially. Chemically the soils contain a very large percentage of silica which com^, first, from the flint, which is abundant in the limfestone, and, second, from the clay which is a hydrous aluminous silicate.