changes in the data which he used and have necessitated a modification of his results.

Since the discharge returned to Port Huron the St. Clair River has cut down its bed about 15 feet and the Detroit River half that amount. This has greatly reduced the effect of drowning of tributaries which was produced at first by the return of the full volume after the period of abandonment during the time of the Nipissing Great Lakes.

In the basins of Lakes Erie and Ontario there are many evidences which indicate recent raising of the water level, such as the drowned stream courses and submerged stumps in Sandusky Bay. These facts seem at first to suggest that tilting of the land was very recent or may still be in progress. But the drowning effects in these two basins, at least to depths of 10 or 15 feet, are probably due to the return of the large volume of discharge at Buffalo and Ogdensburg after the relatively long period of small discharge during the time of the Nipissing Great Lakes, and not to recent or progressing uplift of the land.

POST-GLACIAL MARINE WATERS IN THE OTTAWA AND ST. LAWRENCE VALLEYS AND IN THE LAKE ONTARIO BASIN.

When the ice sheet withdrew from the basin of Lake Ontario and the northern slope of the Adirondacks the sea entered in its place and covered a large area. Its approximate limits (fig. 6) are indicated by postglacial clays, gravels and sands, which are fossiliferous, and the life remains are largely of marine organisms such as are now living in the Gulf of St. Lawrence. The upper limit of the marine waters was about 350 feet at Plattsburg, N. Y., and 523 feet at Covey Hill, Ontario. It was at least 460 feet at Welsh's Siding near Smith's Falls, Ontario, and may have been much more, for at the last-mentioned place the remains of a whale were found in a gravel bed many years ago, and a minimum upper limit of marine submergence is definitely fixed by this occurrence. The height of marine submergence at Montreal is reported to be about 625 feet. On the south side of the St. Lawrence River a well-defined beach marks what is taken to be the upper limit of the marine waters, and has been called by Gilbert the Oswego beach. It declines gradually toward the southwest and passes under the present level of Lake Ontario about at Oswego.

The changes in the level of the waters in the Lake Ontario basin have not been fully worked out, but the marine waters appear to have entered it some time in the later part of the Port Huron stage of Lake Algonquin. The marine connection was through a strait 25 or 30 miles wide and, except for a relatively narrow central depression, not over 40 to 50 feet deep. The uplift appears to have been

85360°-SM 1912-22

and at the end of Lake Algonquin sea level probably did not extend

above Cornwall and Pembroke.

FIG. 10.-DIAGRAMMATIC RELATION OF HINGE LINES AND ISOBASES TO ICE BORDERS, OLD-LAND AREAS, AND LAKE BASINS.
By Frank B. Taylor and Frank Leverett, 1912. (Compiled from various sources.)

The strait was soon raised above the sea, in progress when the sea entered, and the duration of the marine

connection was short.

The accompanying diagrammatic map (fig. 10) shows the relation of the Whittlesey and Algonquin hinge lines to the extreme border of the Wisconsin ice sheet, with three later critical positions of the ice border and several of the isobases. The hinge lines and isobases in the regions east and west of the Great Lakes are added in order to show the general relations of the deformations in those parts to that of the region under discussion. The shore lines of the glacial Lake Agassiz are taken from Upham. (Monograph 25, U. S. Geological Survey.) No shore lines in the Great Lakes area are shown excepting the Glenwood or highest beach of Lake Chicago, the Whittlesey beach, and the correlative beach of Lake Saginaw. The two hinge lines for Whittlesey and Algonquin represent the isobase of zero for each beach. Both are produced conjecturally northwestward to the region of the glacial Lake Agassiz. Two Nipissing isobases are shown in the Superior basin, and these show a trend quite different from those of the Algonquin. In the Michigan and Huron basins the Nipissing beach seems to hinge on about the same line as the Algonquin. The curved isobases in the region south of St. Lawrence River and east of Lake Ontario show the present state of knowledge concerning the deformation of the marine shore line. They show the general relation of the deformation of the marine area to that of the Great Lakes region. The extent of the pre-Cambrian or Old-land area is also indicated to afford means for comparing it with the area of uplift. Inasmuch as the uplift occurred in the course of the melting of the Wisconsin ice sheet and relief from the ice load, and inasmuch as it lies so largely within the glaciated district, a causal relation has by some been inferred and definitely announced. The writer would caution against too hasty conclusions in this matter, especially in view of somewhat discordant relations between the boundaries of the ice and of the uplifted lands which this diagrammatic map will serve to bring out. The writer will take space here merely to state that the preponderance of present evidence appears to be only slightly in favor of resilience following depression by the ice weight as the main cause of the uplifting of the land and the deformation of the shore lines in the region of the Great Lakes. Standing as a close second to the hypothesis of ice weight is the possibility of deformation of the beaches by uplifts of the land incident to crustal creeping movements, which are simply the most recent impulses in a long process of continental growth reaching back into the Tertiary age. If certain evidences which are now supposed to indicate relatively recent crustal creep toward the southwest are substantiated, the hypothesis of resilience following depression by ice weight seems likely to become of secondary importance.

APPLIED GEOLOGY.1

By ALFRED H. BROOKS.2

The science of geology, generally regarded as having originated in the vague speculations of the cosmogonists hardly two centuries ago, has to-day become of great practical utility. During the past decade all geologic investigations have shown a marked tendency toward material problems, which is in contrast with the previous decade, when the interests of pure science were much more strongly emphasized. No one will deny that economic or, as I prefer to call it, applied geology is attracting more and more attention from professional geologists. It is appropriate that the members of this society should take cognizance of this trend in geologic thought, analyze the conditions which have brought it about, and decide, it may be, whether it makes for the good or the evil of the science.

Before discussing this subject it will be well to attempt a definition of the term "applied geology." Some appear to believe that when the geologist emerges from the tunnel's mouth he is at once transplanted into the realm of pure science, and that the miner's candle illuminates only the so-called practical, or even commercial, problems. I submit that such opinions are not justified. The surveys made as a basis for geologic maps and structure sections, usually classed as belonging to the realm of pure science, often yield results which are the most concrete examples of applied geology. On the other hand, the exhaustive study of mineral deposits is essential to the solution of many fundamental geologic problems. A close analysis will make it evident that the line of demarcation between the fields of pure and applied geology is, in a large measure, arbitrary. The collection to-day of a new group of facts or the determination of new principles relating to pure science may result to-morrow in their application to industrial problems. Mr. Gilbert has recognized two fields of geologic research, the one embracing the study of local problems of stratigraphy, structure, etc., the

1 Presidential address delivered before the Geological Society of Washington, Dec. 13, 1911. Reprinted by permission, with author's corrections, from Journal of the Washington Academy of Science, vol. 2, No. 2, Jan. 19, 1912, pp. 19-48.

Published by permission of the Director of the United States Geological Survey.