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16. Manual of Introductory Chemical Practice, for the use of Students; by GEORGE C. CALDWELL, S.B., Ph.D., Professor of Agricultural and Analytical Chemistry, and ABRAM A. BRENEMAN, S.B., Assistant Professor of Applied Chemistry in Cornell University, Ithaca, N. Y. Published by the authors. 124 pp. 12mo. 1875. This manual is an experiment on the part of the authors in a novel mode of chemical instruction, devised by them, with a view to cultivate on the part of the student habits of careful observation, attention to and appreciation of phenomena, and the deduction of legitimate results. In short it seeks to make the student his own teacher by simple synthetic or analytic experiments, and to lead him on by easy steps to an understanding of principles and of chemical philosophy-in a way unattainable from textbooks alone. The student is required to give his results and conclusions in writing, an excellent way to secure accuracy and conciseness of statement. He is presumed to be in attendance on a course of experimental lectures, and to be reciting at the same time from a text-book. The work bears marks of careful preparation.

17. Note on the Electrical Conductivity of Saline Solutions; by J. G. MACGREGOR, M.A., B.Sc., Communicated to the Royal Society of Edinburgh, May 17, 1875; by Professor TAIT (Proc. Roy. Soc. Edinb., 1875, 545.)-This note is a reply to criticisms by Professor Beetz published in the Sitzungsberichte of the Berlin Academy (and in Poggendorff's Annalen) on a paper of Mr. MacGregor's published in the Transactions of the Edinburgh Royal Society, xxvii, pp. 51-70. Mr. MacGregor shows that the criticisms are based in part on a misunderstanding of his paper and of his method of experimenting.

II. GEOLOGY AND MINERALOGY.

1. Supposed Agency of Ice-Floes in the Champlain Period; by Professor A. WINCHELL, Syracuse, N. Y.-I have lately discovered some new instances of huge limestone masses, anomalously detached from the formation to which they belong; and have embraced references to localities, in a paper read before the American Association at Detroit. These are masses of Carboniferous limestone from 10 to 60 feet in length and often of unknown thickness, floating in the sands of Oceana county, apparently 100 or 200 feet above the bed rock. Some of these, I feel constrained to believe, must be genuine exposures of the formation, in place; but others, by being worked out, or by their downhill dip, far exceeding, and disagreeing with, the normal dip of the formation, are demonstrably dissevered and displaced portions of it. For example, one region of exposures of this class in the town of Claybanks, is within half a mile of the shore of Lake Michigan, where we have a bluff 250 feet in height, and attaining, a few rods back, an elevation of 275 feet, serving as a station of the U. S. Lake Survey. The vicinity, for miles around, is elevated 250 to 300 feet above the lake.

But the section of materials exposed in the bluff upon the lake shore is wholly Post-tertiary. It consists of intimately mingled sand and clay, confusedly stratified above, horizontally stratified lower down, and followed downward by an increase of argillaceous material and pebbles, interrupted by a bed of bowlders, beneath which for 10 feet is a mass of bowlder clay seen above a lake-border talus of ten feet. According to the prevailing constitution of the drift of the Peninsula, there should lie, still lower, a thick bed of fine, horizontallystratified clay, with few pebbles, resting on a bottom-sheet of pebbles and bowlders. The drift here is presumably not less than 300 feet thick. Now it is possible that, 2,500 feet back from this bluff, the bed-rock should appear at the surface: but my experience in Michigan strongly inclines me to believe that such is not the fact; and that hence, the numerous outcrops near the lake are mere detached masses.

We have, then, in Michigan, in regions widely separated, the wellestablished phenomenon of extensive tabular masses of limestone floating in the midst of semi stratified sands, generally believed to have been moved and deposited by an aqueous action, which, obviously, could not have transported at the same time these enormous tables of rock. We have, in addition, in some parts of the State, the evidence that this action was sometimes exerted in a northerly direction. Geological theory must attempt to account for these facts.

The generally accepted doctrine of continental glaciation, recognizes a time when the broad glacier underwent a rapid dissolution. The volume of water arising is believed to have been sufficient to produce a long-continued, torrential flood, which moved and assorted whatever detritus existed in its path. Disregarding the detrital material, which must have originated from atmospheric, pluvial and fluvial action over the preglacial surface, a vast volume of detritus must have been originated during the prevalence of the glacier, and chiefly through its action. Most of this must have rested at or near the bottom of the glacier; but probably no small portion had become incorporated with the ice, or intruded into its fissures, or deposited upon its back. The first glacial film embraced the original projections of the ancient surface, which, with the movement of the glacier, must have been displaced to become ultimately a part of the glacier debris. These and the materials derived from sub-glacial detrition must have found their way, to some extent, into the bottom crevasses caused by any diminution in the steepness of the slope down which the glacier moved, and still more when, as was often the case, the change of slope became, in reality a northward declivity. These ordinary conditions of the continental glacier-but feebly represented in the steeper slopes and narrowed limits of modern glaciers-must have resulted frequently in extensive disruptions of the ice, faintly typified in the pyramids and seracs of the Alpine ice-streams. Such upheavals of the lower beds-still more, occasional complete overturnings of portions of the glacier, must have brought considerable earthy detritus to

the very surface of the glacier. In the process of ages, as the ice may be supposed to have gradually diminished, through evaporation, if not through thawing, the superficial earthy material, which never evaporated, must have accumulated to a large extent. How

ever we account for this fact, every one knows that human bodies or other objects, accidentally lost in the glaciers of Mont Blanc, reappear at the surface after a series of years, at points some thousands of feet below.

I infer, therefore, that the material moved by the diluvial waters may have been afforded by some of the interior portions and even the surface of the glacier, as well as by the subjacent rock-rubbish. I will only add that some portions of the material in and upon the ice may have been let down in situ by the slow disappearance of the glacier, without having been subjected to the assorting action of the glacial torrents.*

This process is impressively illustrated along the borders of the Mer de Glace and other Alpine glaciers; and more instructively still in the buried glacier stumps found in the gulches of the Sierra Nevada, and elsewhere in the Pacific States.

I know of no certain evidences, in Michigan, of a Champlain depression of such extent as to bring the surface of any portion of the State below the sea-level. In a district so nearly horizontal, however, there must have been a period, before the erosions of the modern drainage courses had begun, during which the drainage was exceedingly obstructed and slow. The supply of water from the dissolving glacier was greater than could be discharged through the forming outlets; and the extensive areas must have lain submerged until the deepening of the outlets permitted their drainage. But this period was, by hypothesis, that when a geologic winter was merging into a geologic spring. There was not yet a summer climate; and the annual winter must have congealed the surfaces of the surrounding lakes, and arrested the superglacial torrents, if it did not materially diminish the flow of the subglacial ones.

I think the steps of this reasoning safe and sound. But we have here an overlooked condition of glacial agency in the natural order of sequence, which, it seems to me, is adequate to explain the transpositions of rock-masses to which I have referred. There were regions in these lakes where rocky formations rose nearly to the surface, or projected to a slight extent above it. On the freezing of the watery surface, these would be firmly embraced in the ice. Meantime, as the supply of water is diminishing through the advance of the annual winter, the lake subsides, and the frost takes hold of the exposed rock at a greater depth. But the annual spring and summer return. The supply of water increases, the surface of the lake rises and the floating field of ice lifts sheets of previously half-disjointed limestone, and floats them in the direction whither the current sets or the wind blows. They may be dropped some

*This idea was first impressed upon my attention by my brother, N. H. Winchell, who has studied the Drift with much assiduity. See his papers in Proc. Amer. Assoc., Dubuque Meeting, 1872, and in the "Popular Science Monthly" for June and July, 1872.

miles northward from their native bed, and may lodge upon an accumulation of sand moved by aqueous agencies quite inadequate to move cubic yards of solid rock. I think that ice floes are capable of such work; and I believe it is not essentially different from work in progress in the tracks of Arctic currents in modern times.

The same agency would have picked up and transported the rounded northern bowlders, which we find scattered, also, to some extent, through the same sands.

It could not be expected that the existing configuration of the surface of the State should preserve the features which determined the existence and boundaries of such local lakes as I have supposed; but, after all, are not our existing interior lakelets examples of the same, perpetuated by the delayed erosions of outlets? If it be asserted that neither the less nor the greater lakes are engaged in transportation of limestone masses, in our times, it will be a sufficient rejoinder to remind the reader that the supply of movable masses of limestone must ultimately have become exhausted. Still, it is not a fact that work of this kind has entirely ceased, as any one familiar with the flotsam thrown upon a lake beach will be led to admit.

Nor has time obliterated all traces of that topographical configuration, which in Southern Michigan may have determined an icefloat toward the north. Between Saginaw Bay and the mouth of the Grand River is a broad depression, the highest part of which rises but 72 feet above Lake Michigan. The southern tier of counties in the State presents an elevation of 300 to 600 feet above Lake Michigan. The Corniferous limestone barrier, passing through Monroe and Lenawee counties, still maintains an elevation of 100 to 150 feet above the same lake. Have we not here some vestiges of that ancient conformation of the surface which resulted in a northward drainage into the great channel once intersecting the State, and the northward transposition of ice-born sheets of limestone and sandstone, wrenched from the elevated barriers in Hillsdale, Lenawee and Monroe counties, and the contiguous portions of Ohio and Indiana ?

2. On the outlet of the Great Salt Lake; by Professor G. K. GILBERT. (Letter to J. D. Dana, dated Washington, Feb. 4, 1876.)— I had not seen Mr. Packard's paper, when my attention was called to it by your letter of the 29th ult. Since he had "not observed personally any facts bearing on the subject," but merely advanced the ideas of others, it is not surprising that everything which is novel in his paper is erroneous.

When the water of Great Salt Lake was at its maximum altitude it carved and molded a beach, which yet remains-a conspicuous monument to its former greatness. Within the circle of this beach-line are included also Utah and Sevier lakes. The level of the ancient beach is 970 feet higher than Great Salt Lake, about 700 feet higher than Utah lake, and about 550 feet higher than Sevier Lake. From the upper beach the water slowly subsided by desiccation, recording its lingerings in a series of fainter

shore-lines. When it had fallen to the level of the divide between the Sevier and Salt Lake basins, it was separated into two unequal portions. In one of these the evaporation exceeded the inflow from rivers, and the subsidence continued; in the other the inflow exceeded the evaporation and the surplus was discharged over the divide into the former portion, just as the surplus of Utah Lake is now discharged into Great Salt Lake. In the course of time, as the climate became drier, this overflow ceased; but not until it had carved a channel of some magnitude. The channel is crossed by the old overland stage road, and is known as "the Old River Bed." It is doubtless this ancient water-way which has been described to Mr. Packard. I am not aware that it has ever been determined whether the channel slopes toward Sevier, or toward Great Salt Lake; but a consideration of the forms and dimensions of the two basins, and of the present relative salinity of the two lakes, leads to the belief that it was the Sevier Basin which overflowed into the other. The summit of the divide cannot be far above the present level of Sevier Lake.

In the early part of the field-season of 1872, I crossed the Salt Lake and Sevier deserts as a geologist of the Wheeler Expedition, and gave especial attention to the beaches and other phenomena of the ancient lake. Later in the season my associate, Mr. Howell, carried the observations farther south. Ŏur examinations were sufficiently thorough to enable us to draw a map of the southern half of the old lake, but we found no evidence of an outlet in that direction, although we made diligent search. According to the conjecture of Professor Bradley, and the unpublished observation of Professor Marsh, the overflow was northward, and the Columbia River carried the water to the ocean. There assuredly was an overflow.

In the progress report of Lieut. Wheeler's Surveys for 1872, I have expressed the opinion that the humid climate which was marked by this inundation of Utah, was preceded by one as arid as the present; and that the humidity was a phenomenon of the Glacial Epoch. A fuller statement and discussion of the facts will appear in the geological volume (now in press) of the reports of the Wheeler Surveys; and the accompanying atlas will contain a map of the ancient lake.

3. Second Report of Progress of the Mineralogical, Geological and Physical Survey of the State of Georgia, for 1875; by GEORGE LITTLE, State Geologist. 8vo, 16 pp.-This brief report shows a large amount of work done during the past year. The several parties have traversed, in all, over 6,000 miles of road, making careful examinations and large collections along their routes. They have visited 105 out of the 137 counties in the State, and a list is given of the minerals, metals and building-stones, of economical value, which have been found in 76 of these counties. Under the head of Geology, Dr. Little says: "In the Northwestern portion of the State, the coal-formation has been found, by Mr. McCutchen, to be somewhat more extensive than observed

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