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BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

VOL. 29, PP. 235-244 JUNE 30, 1918

EXPLANATION OF THE ABANDONED BEACHES ABOUT THE SOUTH END OF MICHIGAN1

BY 0. FREDERICK WRIGHT (Presented in abstract before the Society December 28, 1916) CONTENTS 1 a^e I’eat deposits between the second and third beaches...... 2:iT 23S Supposed changes of land levels...... Supposed earlier opening of the Sat; outlet...... 240 Effects of the diversion of the water in the glacial in the Ei•ie- Basin...... ,241 Glacial and clay deposits underneath Chicago...... 24:; Provisional estimates of glacial time afforded in this area...... 244

D e s c r ip t io n o f t h e B e a c h e s

Three abandoned postglacial beaches at the south end of Lake have been known for many years. In 1870 Dr. Edmund Andrews de­ scribed them in a very elaborate paper published by the Chicago Academy of Sciences. Later, Mr. Leverett, in his monograph, “Illinois glacial lobe,” and Mr. William C. Alden, in his Chicago Folio of the U. S. Geological Survey, have collected the facts in very full measure. From these and other published observations it appears that, surrounding the south end of from about the vicinity of Waukegan, on the west side, and extending indefinitely northward on the east side, there is an abandoned beach approximately 60 feet above the level of the lake. This is called the Glenwood beach. Twenty feet lower, or about 40 feet above the present level of the lake, occurs what is called the Calumet beach. Twenty feet lower still, or approximately 20 feet above the level of the lake, occurs the Tolle-ston beach. These are shown on the accompanying map (figure 1), compiled 1 Manuscript received by the Secretary o£ the Society March 10, 1918. (235) 236 . . RGT------BNOE BAHS BU LK MICHIGAN LAKE ABOUT BEACHES WRIGHT------ABANDONED F. G.

Compiled and drawn by Miss Lonie Shedd. The broken lines south of Galewood and Rosehill moraines indicate the probable extension of those moraines supposed to have been washed down by the waves of . For a description of the beaches, see text. DESCRIPTION OE THE BEACHES 237 from the Chicago Polio of the region south of the lake. All these beaches are interrupted by the Chicago outlet along the line of the present drain­ age canal, this outlet having served its purpose during the formation of them all.

P e a t D e p o s it s b e t w e e n t h e S ec o n d a n d T h ir d B e a c h e s

The facts most difficult of explanation connected with these beaches are the accumulations of beds of peaty material underlying the second (Calu­ met) beach. These were noticed by Doctor Andrews at various places, especially near Evanston, where they not only underlie the second beach, but “extend eastward across the interval between It and the third beach. Its level is no higher than that of the third beach, being only 12 to 15 feet above the present level of Lake Michigan. . . . The peat is immediately overlaid by about five feet of sand, above which there is a bed of coarse gravel. The gravel is thin near the borders of the bar, but has a thickness of 10 or 12 feet at the highest part It is capped by a thin deposit of sand, and has also layers of sand interbedded in its thickest parts. The presence of this gravel makes it certain that the old marshy land surface has not been buried by the drift­ ing of material from the lower beach. There seems no escape from the con­ clusion that the lake stood at a lower stage than the level of the second beach before that beach and the bar under discussion were formed.”2 Also, according to Leverett: 8 “For a few miles in the vicinity of the State line between and Michigan there are exposures of peaty material along the blufE of Lake Mich­ igan at levels ranging from about 15 feet above the lake down to the water’s edge. . . . Near Michigan City peaty layers just above the water’s edge are nearly continuous for a distance of a mile or more and occur at frequent inter­ vals from Michigan City to the Michigan State line. Above the peaty beds pebbly sand in places reaches an elevation of 30 feet above the lake, or nearly to the level of the second beach. The peat appears, therefore, to have been developed prior to the formation of that beach, and probably has the same age as that noted near Evanston, Illinois.” Later, however, in Monograph L III, Mr. Leverett hesitates about ac­ cepting this evidence as conclusive. Speaking of the Evanston peat deposits, he suggests that “a bar might beextended out over a peat deposit standing at the same level as the lake and press it down and thus give it a lower level than it had while in process of growth. At the Evanston locality this interpretation would seem very plausible, for the bar was built out into water of considerable depth by southward-moving currents.” 4 2 Leverett : Illinois glacial lobe, p. 445. » Ibid., p. 445. * Ibid., p. 356. 238 G. P. WRIGHT— ABANDONED BEACHES ABOUT LAKE MICHIGAN I t is difficult to see the force of this suggestion of Mr. Leverett. How could a thickness of 10 or 13 feet of gravel, capped by a thin deposit of sand, be pushed out into water of considerable depth to cover a deposit of peat that was originally at the level of the southward moving currents which deposited the bar? The conception is impossible. We shall be justified, therefore, in accepting the original conclusions of Doctor Andrews and Mr. Leverett, which were formed when these Evanston de­ posits were all exposed. Unfortunately, at the present time the growth of the city has so modified the shore that the facts are not now open to inspection. Speaking further of the peat deposits near Michigan City, he says: “The sand evidently was deposited during the development of that beach and the peat is certainly as old as the beach. The beach may have been ex­ tended out over a peaty deposit, as was suggested in the case of the JJvanston deposits, but the conditions on the whole do not strongly favor this view.” 5 To establish the early date of the peat, Mr. Leverett would demand the discovery of valleys which entered the lake at this lower stage, at a level below the Calumet beach, and which had been built across by the Calumet beach; but in the lack of such evidence it is not necessary to give it much weight.

T he Seeies of Moraines As will be seen from the map, the' outlet has two branches coming to­ gether at the Sag. These are separated by Mount Forest Island, which is in the main a moraine deposit. From the Sag westward through Lemont to Lockport the channel is on a dead level, running over a rock shelf 8 feet above Lake Michigan. At Lockport it descends through Joliet and some distance below, 35 or 40 feet in a few miles. At the foot of this descent there are immense gravel deposits (including many boulders a foot or more in diameter) on the west side of the Des Plaines River, rising 60 feet above the river plane and covering fully a square mile. The gravel is also 40 feet in depth below the river plane. Properly to interpret the history of this outlet, we must consider the series of moraines on the west side of the lake. The outer moraine is many miles in width, extending all around the south end. It is called by Leverett the . North of the outlet there are two or three narrow parallel moraines extending from the north, but at present not reaching the south end of the lake. Numbering from the west, the Gale wood moraine is separated from the Valparaiso moraine by a valley 2 or 3 miles wide, through which the Des Plaines River flows. A little “ Ibid.. p. ?56. THE SERIES OF MORAINES 239 farther east the Rose H ill moraine is found, but does not at present pro­ ject quite so far south. The space between this and the Galewood mo­ raine is occupied by the Chicago River. Going farther north, there are remnants of a parallel moraine above Evanston. These all seem to be lateral moraines formed when the ice in shrunken quantities extended toward the south end of the lake, but the erosion of the water has very likely removed their extreme southern ends, so that their existence can only be inferred; but Mr. Lcverett thinks it not at all improbable that the Rose H ill moraine extended southward to Blue Island, which is cer­ tainly a moraine formation 6 miles long, since the rock does not appear underneath it until a depth of 50 or GO feet is reached, while it rises more than 60 feet above the lake level. It would seem also likely that the Galewood moraine extended to Mount Forest Island, which is deeply covered with moraine material. As a partial proof of this, it is to be noted that the 60-foot terrace extends southward from Galewood through Oak Park well on toward Mount Forest Island.

H ist o r y o f t h e C h ic a g o O u t let It is true that this 60-foot beach through Oak Park, like the 40-foot beach which extends toward Blue Island, is composed of stratified sand and gravel; but as the erosive agencies of the lake when at its higher levels probably operated for several thousand vears, and as these agencies are known at the present time to be eating into the bank at rates varying from 2 to 3 feet a year, there was ample opportunity for them to level these narrow moraines and so in part to account for the material forming the present Glenwood and Calumet beaches in that vicinity. But this is preliminary to considerations bearing on the opening of the outlet followed by the Drainage Canal and the Des Plaines River. This channel, as well as both the Sag and Des Plaines outlets which join to form it, is from 1 to 2 miles wide, with rocky sides rising at La Grange, on the north, 60 feet above the lake, and at Lemont, on the south side, to the same height. Farther in the interior moraine deposits rise to a height of 160 feet above the lake. The level of the rock bed of the outlet, as already said, is 8 feet above the lake. Two suppositions have been resorted to in accounting for the accumu­ lation of peat underneath the Calumet beach. Mr. Alden suggested that the water fell to the level of the Tolleston beach by being drained off eastward as the ice had receded and opened up channels in that direction, and that this continued for sufficient time for the peat to accumulate, when a readvance of the ice closed up those outlets and raised the water 240 G. P. WRIGHT— ABANDONED BEACHES ABOUT LAKE MICHIGAN to a 40-foot level. Others resort to the supposition that there was an elevation of the land north of the outlet sufficient to allow the accumula­ tion of peat, and that afterward there was a depression to the Calumet level. The only direct evidence supposed to indicate such a temporary land elevation is drawn from soundings in various narrow lakes tributary to Lake Michigan on the east side, which in several cases descend at least 50 feet below the present level of the lake. But it would seem altogether probable that these are preglacial channels or depressions preserved, by the presence of ice, from being filled with glacial material.

S upposed Ch a n g es op L a nd L evels A recent survey of the whole region, under the guidance of Mr. Charles B. Shedd, suggests a theory which avoids the obvious difficulties con­ nected with the other theories and is supported by all the facts and causes known to be in operation. The 60-foot water level, during which the first beach was formed, is accounted for by the natural supposition that the drainage outlet from Summit to Joliet was filled with glacial deposits, compelling the water to rise to that level. Naturally the clearing out of this channel would take place by a process that is called “stoping”—that is, by a wearing back from the Joliet end by a recession somewhat similar to that which takes place in waterfalls. Otherwise there would have been a succession of numerous small beaches. Their absence shows that the water was kept up to the 60-foot level until the removal of the obstruction through its whole extent, constituting the Glenwood period. Very interesting Glenwood dunes are to be seen on the west side of Blue Island, already referred to as a narrow mass of morainic character, some 5 or 6 miles in length, that stood above the 60-foot level of the lake. These were evidently formed out of the shallow water deposit to the west during the Glenwood stage, as is shown by their long slope to the west and their abrupt slope to the east; they are of finer material, more oxidized than most of the other dunes, and now covered with grass and large trees.

S upposed earlier Op e n in g of t h e S ag Outlet Mr. Shedd has suggested that naturally the Sag outlet was opened before the Des Plaines River outlet to the north of Mount Forest Island, which he thinks was probably closed during the Glenwood stage by the prolongation of the moraine from Galewood down to Mount Forest Island, probably maintaining the Sag outlet to the 60-foot level during EARLIER OPENING OP THE SAG OUTLET 241 the Glenwood stage, and that while the Des Plaines River from the north was digging and deepening its channel on the west side of the moraine and to the Sag and beyond, that the east side of the moraine was being washed down and spread out by wave action, as was the case all along the west shore of Lake Michigan, for nearly a mile in width, until it was washed down, and the 60-foot waters of Lake Chicago suddenly rushed through into the deepened Des Plaines Channel, lowering the water level to the 20-foot Tolleston stage, when little or no water passed through the narrow Sag Channel, afterward widened out by the long-continued deeper flow of the Calumet stage. This is a plausible theory if it can be substantiated and proved by fur­ ther examination. In any event it seems quite evident that the water was in some way lowered down quickly to the 20-foot Tolleston stage and maintained there long enough for the formation of the peat beds that have been referred to.

E ffects of t h e D iversion of t h e W ater in t h e glacial L akes in t h e E r ie-O ntario B a sin A natural explanation of the long-continued 40-foot water level pro­ ducing the second, or Calumet, terrace is found in the immense accession of water to the south end of Lake Michigan from the glacial lake which had been ponded in the Erie-Huron-Ontario Basin, which covered many thousand square miles and was at first approximately 200 feet above the present level of Lake Michigan. This body of water having its outlet at first into the Basin through a well defined channel at Fort Wayne, Indiana, was lowered at successive stages as the ice receded northward. First, there was a fall of approximately 50 feet when the Imlay outlet across the thumb in Michigan was opened into the Valley, and another 50 feet when the Ubly outlet farther north was opened by the retreating ice, and, according to Mr. Taylor’s estimates, another 20- foot fall when the ice had receded beyond the thumb, letting the waters of through into the Grand River Valley. These three stages of water, named successively , , and Lake Warren, are clearly marked by abandoned shore­ lines on the south side of . A beach 200 feet above Lake Erie leads around to Fort Wayne, where it is interrupted by the channel of the original outlet and resumed again on the other side. The 150-foot beach leads around to the Imlay outlet and the 100-foot beach around to the Ubly and Saginaw outlets. This would still leave an enlarging basin of water, covering many thousand square miles, 70 feet above the Chicago outlet, continuing until 2 4 2 G. F. WRIGHT----ABANDONED BEACHES ABOUT LAKE MICHIGAN the ice had receded beyond Mackinac, when it would pour through the straits to Lake .Michigan, though there may be some doubt as to when the outlet through the Mohawk Valley to the east was so opened as to take off a part of this lower accumulation. The opening through the Mohawk Basin and Niagara gorge at last would bring the water down to its present level.

...... - Boundary of lakes Maumee and Whittlesey and the Imlay outlet into Lake Michigan ...... Boundary of Lake Warren, with its Ubly and Saginaw outlets into Lake Michigan Compiled and drawn by Miss Lonie Shedd. Fort Wayne, outlet into the of Lake Maumee, about 200 feet above Lake Erie, as glacier ice-front receded. Imlay. outlet of Lake Maumee through Grand River down to level of Lake Whittlesey, about .150 feet above Lake Erie. Ubly, outlet of Lake Whittlesey through Grand River down to level of Lake Warren, about 100 feet above Lake Erie. Saginaw Bay, outlet of Lake Warren through Grand River to about 70 feet above Lake Erie. That this influx of water from the would be sufficient to raise Lake Chicago to a 40-foot level is easily believed when we con­ sider the size and depth of the outlet at Fort Wayne and the extent of the glacial lakes which occupied the Erie-Ontario Basin. The old outlet, now occupied by the major portion of the city of Fort Wayne, is nearly 2 miles wide and 20 feet in depth, such a channel having been necessary to' carry off the surplus water from the melting ice to the northward. When the opening into Lake Chicago through the Grand River valley occurred, all this surplus water, as well as that ponded up to the 200- CHANGES IN THE CHICAGO OUTLET 2 4 3 foot level in the Lake Erie Basin, would have to find its way through the Chicago outlet. No one who examines the facts can hesitate to believe in the sufficiency of this water supply to produce the known results. Tt is fair to say that this explanation is suggested in a single sentence by Mr. P. B. Taylor on page 326 of Monograph LIII, where he says: “The changes which occurred in Lake Chicago were due to erosion of its outlet or to changes in the volume of its discharge.”

G l a c ia l a n d C la y D e p o s it s u n d e r n e a t h C h ic a g o Mr. Shedd calls attention to a deposit of soft putty-like blue clay that overlies the hard-pan glacial drift underneath all the Chicago region, wherever caissons have been sunk or channels dug. Prom information furnished by Mr. George W. Jackson, who has built 110 miles of tunnel under the city of Chicago, and from Mr. John Griffiths and other engineers who have sunk innu­ merable caissons to the solid rock for the support of the great build­ ings of the city, we learn that be­ low a few feet of muck and yellow loam, which form the surface de­ posit over this area, there is regu­ larly from 20 to 40 feet of soft blue clay resting on the till, which extends in most cases about 60 feet farther down to the solid rock, which in many cases shows grooves and stretches character­ istic of glacial surfaces. Mr. Griffiths gave me a piece of copper which he had found a few days before, 60 feet below the surface, in a caisson F ig u r e 3.— Section of laminated Clay above which he was sinking at the cor- the- »»It blue Clay appearing in the diver- ner otp TTHarrison and Canalri streets. iii sion Channel at Evanston. Mr. Jackson reports that beneath the till over the hard limestone rock there frequently occurs ’a stratum 3 or 4 inches thick of “black torpedo gravel from the size of a pinhead to a pea.” This succession of deposits continues substantially the same 2 or 3 miles out into the lake east of Jackson Park, where he put in the Hyde Park water works tunnel and crib. Mr. Shedd also reports a similar succession at Wolf Lake, in the 244 G. P. WRIGHT— ABANDONED BEACHES ABOUT LAKE MICHIGAN southern extremity of Chicago, and at Uvanston, north of the city, where the new diversion channel is in process of construction. A photograph of a section of the deposit is here shown (see figure 3). The significance of this with reference to the raised beaches under consideration is easily seen. The few feet of clay muck and yellow loam covering the surface is evidently a deposit connected with the Tolleston beach or the Calumet beach, both deposited after the Glenwood stage. The thick deposit of soft blue clay underlying it must have taken place in the deep water which prevailed during the formation of the Glenwood beach. More careful and extensive study of these deposits is required to determine the length of time required for their deposition. As near as we could esti­ mate, there are 100 of these clay laminae to the foot in the upper deposit.

P rovisional E stim ates of G lacial T im e afforded in t h is A rea

Assuming that each of the laminae represents an annual deposit, which, however, is by no means certain, that would give 4,000 years for the con­ tinuance of the Glenwood stage of water. This calculation is roughly approximate to that made from deposits in the bottom of Lake Maumee, in the Lake Erie basin, where 35 feet of fine sediment had accumulated in lamina which numbered 8 to the inch. These calculations, also, roughly approximate those made by Doctor Andrews concerning the time required for the accumulation of the dunes at the south end of Lake Michigan, which he estimates to be 6,000 years, though later authorities have, however, questioned the correctness of some of his data. All this, however, precedes the time during which Lake Michigan has occupied its present level, determined by the eastward drainage of its waters. The most promising method of estimating this time is presented in the estimated amount and rate of the erosion of its western banks by the waters of the lake. The extent of this erosion is revealed by the width of the shallow shelf covered by about 60 feet of water, which ex­ tends out to the deeper depths of the lake. Assuming that the margin of these 60-foot soundings follow the old shoreline, which is now at an average distance of 2.72 miles from the present shore, and that the rate of erosion (3.33 feet) determined by the Wisconsin Survey is correct, the age of the present lake would be only 4,708 years. Granting that these estimates are at the best only a $ude approximation, Mr. Leverett concedes that they “have much value in their bearing on the length of postglacial time,” and quotes with approval Doctor Andrews’s remark “that they are useful in showing that it is impossible to allow, even on the most liberal estimates, any such postglacial antiquity as 100,000 years, which has often been claimed.” ’ «Illinois glacial lobe, p. 459.