April 14, 1898] 



NATURE 



573 



not now live in Canadian waters, but are found in the Mississippi ; 

 and several species of trees now belonging to the States to the 

 south occur with them, indicating a climate decidedly warmer 

 than 'the present. Above this come stratified clay and sand, 

 with a caribou horn and remains of insects and plants belonging 

 to a colder climate than the present. This set of clays and sands 

 is best shown in the clift'-section at Scarborough Heights a few 

 miles to the east, where the series rises 148 feet above Lake 

 Ontario, and contains many species of extinct beetles, as well as 

 shell-fish, mosses, and wood of hardy trees. A complicated 

 middle till overlies these beds which were deeply eroded before 

 the advance of the ice. Another less important fossil-bearing 

 bed occurs above the middle till at elevations up to 240 feet 

 above the lake, and is followed by a third till. Prof. Coleman 

 notes that great changes have occurred in the level of the water, 

 the lake being much lower than at present before the first glacial 

 advance and after the first interglacial time, and that during the 

 deposition of the middle till, and also while the last sheet of 

 till was being deposited, the water stood from 250 to 300 feet 

 above the present level of the lake, which is 247 feet above the 

 sea. In his opinion the length of time required for the first 

 interglacial period is probably to be estimated at thousands of 

 years ; and during this time he thinks the ice-sheet of the 

 Laurentide Glacier must have completely disappeared. 



As a result of this paper a British Association Committee was 

 appointed to investigate these deposits further by means of 

 excavations. The palseontological evidence is held to imply 

 that, as above stated, the climate when the Don Valley deposits 

 were laid down was such as would be incompatible with the 

 presence of ice anywhere in the Laurentide area, and that this 

 warm period was followed by a later glaciation, of which the 

 clearest evidence is contained in the section at Scarborough 

 Heights. The identification of the warm-climate horizon in this 

 cliff-section is especially desirable, and is one of the results which 

 may be: hoped from the Committee's investigations. 



In describing the drift phenomena of the Pacific coast around 

 Puget Sound, which in most respects compare very closely with 

 those of our own islands, Mr. Bayley Willis put forward the 

 hypothesis that the channels of the Sound, which have usually 

 been considered submerged valleys, are the hollows remaining 

 after repeated glacial invasion of a wide and diversified de- 

 pression, during which the earlier divides were built upon, and 

 transformed into plateau like eminences of glacial drift, whereas 

 the occupation of the valleys by glacial ice, particularly in 

 the stagnant stages of retreat, prevented their being per- 

 manently filled ; so that with the final retreat of the ice the 

 moulds of glaciers remained as the channels of the Sound. 



This view accentuates the undoubted fact that the accumula- 

 tion of glacial debris has been greater around the margins of the 

 old ice lobes than in the more central areas, and it may be applied 

 to some extent to our own islands, where the persistence since 

 pre-glacial times of the shallow basins of the North Sea and the 

 Irish Sea appears to indicate that a larger proportion of the 

 material transported by the ice-sheets which once filled them 

 has been deposited around their margins than within their beds. 



The old lake-beaches, incidentally referred to by Prof. 

 Coleman and Mr, Tyrrell, occupy a large place in the studies of 

 the American glacialists, while in the British islands, in spite 

 of the rough pion£er work of the late Prof. Carvell Lewis, the 

 subject has scarcely been touched. The scope for these 

 researches in our country is, of course, limited ; but the classical 

 example of the parallel roads of Glen Roy is sufficient to prove 

 that the phenomena are not unrepresented. In America two 

 distinct types of old lakes have been recognised — those like 

 Lake Agassiz and Lake Warren, which were formed in front 

 of the retreating ice-margin, and those like Lake Nipissing and 

 Lake Iroquois, which owed their position to differential earth 

 anovements. 



The literature in regard to both types is already very exten- 

 riive, and is not altogether satisfactory. Especially in the case 

 of the glacially-dammed waters, their reputed vast extent, their 

 impersistence of level and brief duration, the later modifi- 

 cation of their sites by earth movements, and above all the 

 obscurity of their traces over wide tracts of uncleared forest, 

 makes it certain that while the broad fact of their former exist- 

 ence maybe undoubted, the delimitation and correlation of their 

 boundaries must be regarded in most cases as more or less pro- 

 visional. With gravelly deposits of all kinds spread 'over such 

 an enormous extent of territory it must nece.ssarijy be difficult 

 to pick out an individual shore-line unless this can be traced 



NO. 1485, VOL, 57] 



almost continuously, which is rarely possible. In certain 

 regions, however, the study has been carried on under more 

 favourable conditions, with most interesting results. Thus Prof. 

 H. Leroy Fairchild, in describing the glacial phenomena of 

 Western New York,i showed how the long upland valleys of 

 that part of the State contain the terraces of lakes which 

 have overflowed southward across the watershed, leaving well- 

 marked channels of glacial drainage, and how as lower passes 

 were opened by the retreating ice the waters of these lakes sank 

 to corresponding levels. The highest of the continuous shore- 

 lines of this region is recognised as being that of the glacial Lake 

 Warren, which is believed to have stretched from the western 

 end of the basin of Lake Ontario over the whole or the greater 

 part of the Great Lakes. ^ 



Below this are found several less continuous terraces, probably 

 marking different stages of the depletion of the lake, until at about 

 500 feet lower the Iroquois shore-line is reached, which appears 

 to have been the immediate forerunner of the Lake Ontario of 

 the present day. This beach is admirably developed in the 

 vicinity of Toronto, and the main facts regarding it were de- 

 monstrated by Mr. Gilbert and Dr. Spencer during the meet- 

 ing. Dr. Spencer considers that it is an old sea-beach ; but in 

 this he is at variance with most of the American glacialists, who 

 hold that it, like the higher beaches, is of fresh-water origin. 



These old beach-lines are of especial importance in that they 

 reveal considerable differential uplift during late-glacial and post- 

 glacial times. On this point all the students of the subject are 

 agreed, and it is, of course, regarded therefore as a factor of 

 prime importance in the later history of the lake basins. It was 

 insisted upon by Mr. F. B. Taylor in an interesting communi- 

 cation on the relation of the Champlain submergence to the 

 Great Lakes and to Niagara Falls. Working on the same lines 

 as Mr. Gilbert had done, Mr. Taylor showed that an old shore- 

 line, named the Nipissing Beach, surrounds a large portion of 

 the Upper Great Lakes, and leads to a low col at the east end 

 of Lake Nipissing. The formation of this beach he supposes 

 to have been contemporaneous with the Champlain submergence 

 by which the St. Lawrence Valley and the Champlain depres- 

 sion became arms of the sea, so that during this period the 

 Upper Great Lakes had their outlet by way of the Nipissing 

 Pass and the Ottawa River into the St. Lawrence, leaving only 

 the discharge of Lake Erie, or one-ninth of the total volume, to 

 occupy the Niagara River. Mr. Taylor stated that the Nipis- 

 sing beach is tilted so that it falls regularly towards S. 27 W. at 

 the rate of nearly 7 inches to the mile, being no to 115 feet 

 above the present surface of the north-eastern part of Lake 

 Superior, while not far east of Duluth it has sunk to the water 

 level, and if its plane were projected it would pass 100 feet 

 below the lake-level at Chicago. Pie gave reasons for consider- 

 ing that the tilting was caused by the same uplift which raised 

 the Champlain Valley, and that one effect of this movement was 

 to close the Nipissing outlet and to open that at Port Huron, by 

 which the entire discharge of the lakes was sent into the 

 Niagara. The result of these changes is to be found, accord- 

 ing to Mr. Taylor, in the caiion below the Falls, the narrow and 

 shallow gorge of the Whirlpool Rapids indicating the work of the 

 comparatively feeble stream from Lake Erie, while the Upper 

 Great Gorge has been excavated since the closing of the Nipis- 

 sing outlet, which, accepting the known rate of recession of the 

 Horse-shoe Fall as the principal datum, may have taken place 

 from 5000 to 10,000 years ago. 



These researches may well serve to illustrate the complexity of 

 the problem whenever an attempt is made to transmute the term 

 of geological processes into an equivalent in years. Simple 

 multiplication and division without a steady-going chronometer 

 can never suffice, nor is the time-unit that serves for a man's life 

 ever likely to help us much in measuring the duration of cosmic 

 processes. 



As regards the differential movement, Spencer and Gilbert 

 are of opinion that it is still in progress, and will eventually sub- 

 merge Chicago and dry up Niagara. In a recent paper * Gilbert 

 has even ventured to predict in years when this may be expected. 



G. W. L. 



* 1 This paper is printed in full in the Geological Magazine, and is 

 therefore easily accessible to British geologists. 



- An admirable summary of the work of Spencer, Gilbert, and others in 

 elucidating the history of this great body of water will be found in a paper 

 by Mr. Warren Upham on " Glacial Lakes in Canada," Bull. Geol. Soc. of 

 Am., vol. ii. (1891) pp. 243-276. 



3 " Modification of the Great Lakes by Earth Movement," U.S. Nat. Geo- 

 graphic Mag., vol. viii., September 1897, p. 2s? (see Nature, December 

 301 1897). 



