612 



SCIENCE. 



[N. S. Vol. IV. No. 95. 



strata, between the rising upper Devonian 

 inface that ascends to the Alleghany plateau, 

 on the south, and the falling Niagara inface 

 that descends, on the north, to the Ontario 

 plain, the latter being another inner low- 

 land of the very ancient coastal plain of 

 which the Laurentian highlands of Canada 

 are the oldland.* A large part of these 

 inner lowlands is under the water of the 

 lakes, but where emerged they support a 

 thriving agricultural population ; fruit be- 

 ing extensively cultivated on the Ontario 

 plain north of the Niagara infacing escarp- 

 ment (locally known as ' the mountain'; 

 a good illustration of the geographical 

 poverty of our language) , as well as on the 

 Erie plain. Although the ancient lake 

 shores hereabouts are characterized by 

 gravel bars, the present Erie shore is 

 mostly a cliff, cut in shales. Besides the 

 reasons suggested by Tarr for this contrast, 

 the greater time of action at the present 

 level may be considered. The ancient 

 shore lines of Lake Erie in the fruit belt 

 did not advance beyond the youthful stage 

 of building off-shore bars on a shallow bot- 

 tom. The present shore lines have advanced 

 to the mature stage of low cliffs cut into the 

 gently sloping mainland. Whether the 

 present shore lines went through the pre- 

 paratory phase of building off-shore bars 

 cannot be said without further study, but 

 there does not appear to be any reason why 

 they should not have witnessed all the nor- 

 mal stages of shore-line development up to 

 their existing maturity. 



THE GORGE OF THE AAE. 



A. E. Wallace, an earnest advocate of 

 the glacial origin of lake basins, illustrates 

 the competence of ice streams to erode rock 

 basins by the relation of the gorge of the 

 Aar, cut through a rocky barrier that trav- 

 erses its valley above Lake Brienz, to the 



* Oldland, inner lowland and inface are convenient 

 terms in the description of denuded coastal plains. 



broad valley-basin further upstream {Fort- 

 nightly Review, Aug., '96). The basin is 

 covered with a plain of alluvium, estimated 

 to be 200 feet deep. The rocky barrier aver- 

 ages 450 feet higher than the alluvial plain, 

 and is thought to have lost 350 feet of height 

 by glacial erosion. The rock floor of the 

 basin is thus shown to be 1000 feet deeper 

 than the preglacial height of the barrier, 

 and this depth is taken as the measure of 

 glacial erosion above the barrier. 



The extension of valid argument of this 

 kind to the conclusion that all lakes in gla- 

 ciated regions are of glacial origin, seems 

 illogical ; and the derogatory references to 

 the explanation of lakes by subsidence or 

 deformation seems hardly candid in face of 

 the facts reported by many Swiss geologists. 

 Indeed, the generality of glacial erosion in 

 certain regions may be so forciblj^ met by 

 the generality of glacial deposition in others, 

 that lakes must be individually studied if 

 their actual origin is to be explained. The 

 citation of the essays by Lincoln and Tarr 

 concerning the Finger Lakes of New York, 

 and the silence concerning such essays as 

 Aeppli's on Lake Zurich, give Wallace's 

 essay an air of special pleading. 



'aLAI and PAMIR. 



F. DE EoccA summarizes recent explora- 

 tions of the elevated portion of central Asia, 

 in which he has himself taken part (Eev. 

 de Geogr., xix., 1896, Jan., April). The 

 Pamir is described as an immense uplift, 

 trenched by profound valleys, and sur- 

 rounded by colossal mountain ranges ; thus 

 differing from the definition given by Cur- 

 zon (Science, Aug. 21, 1896). The moun- 

 tains are characterized as colossal, gran- 

 diose, imposing ; but relation of form to 

 structure and denudation is hardly touched. 

 The long valleys descend gradually east- 

 ward to the interior basin, but abruptly 

 westward to the open lowlands. The main 

 divides are sometimes on the valley floors. 



