JiXK 14, 1895.] 



SCIENCE. 



G51 



generally discredited, tluiugh he claimed 

 native sources for them ; and it is fair to 

 add that we have no positive certainty how 

 great the value of the mnemonic system of 

 the (iuichiias, their knotted and colored 

 cords, the quipus. may have been. It has also 

 been more than once argued that there must 

 have occurred important modifications in 

 climate since the great temples and cities 

 on the cold plateaus were Ijuilt, and har- 

 bored the large populations which must 

 ha\'e dwelt in them. This would require a 

 long period. 



As Dr. Dorsey speaks from personal ob- 

 servations and extensive arcbieological ex- 

 plorations in Peru, his opinion, however at 

 A-ariance with that usually entertained, 

 merits careful consideration. 



D. G. Brinton. 



University of Pennsylvania. 



CURSENT NOTES ON PHYSIOGRAPHY (IX. ) 

 THE glacial origin OF LAKE BASIXS. 



As LONG as lakes are regarded simply as 

 locally deepened valleys, their explanation 

 by glacial erosion may be fairly maintained: 

 for when the problem is thus vaguelj' stated, 

 the requirements to be met by the theory 

 are so simple that the hypothesis of glacial 

 erosion finds perhaps better reasons for ac- 

 ceptance than any other hypothesis. But 

 as the facts to be explained are more care- 

 fully observed, thej* generally become more 

 highly specialized and more peculiarly cor- 

 related; and their glacial origin may then 

 be either confirmed or excluded. The pe- 

 culiar association of features described by 

 Lincoln (Amer. Jour. Sci., xliv., 1892, 290) 

 and by Tarr (Bull. Geol. Soc. Amer., v.. 

 1894, 339), regarding Cayuga Lake, seems 

 on the one hand to demonstrate the glacial 

 excavation of this Ijasiu; but, ou the other 

 hand, the extraordinary correlation of facts 

 determined Ijy various observers around 

 Lake Zurich does not seem to be witliin 

 reach of explanation by so simple a process 



as glacial erosion. In spite of so good a 

 general argument for the competence of ice 

 action as has been presented by Bohm 

 (Yerein zur Verbreit. Xaturw. Kenntnisse 

 in Wien, xxxi., 1891, 477), and in spite of 

 the emphatic disapproval by J. Geikie of 

 various other processes that have beeu sug- 

 gested for the production of Alpine lakes 

 (Great Ice Age. 3d ed., ch. xix.), the origin 

 of Lake Zurich is certainly not to be ac- 

 counted for by generalizations at a dis- 

 tance, l)ut only by a special process that will 

 fit all the facts found on the ground. Evi- 

 dence tending to this end has gradually been 

 accumulating for a number of years : but at 

 an accelerated rate since Heim and Bodmer 

 interpreted the meaning of the rock teh- 

 races on the vallej- sides, and since Penek, 

 DuPasquier and others deciphered the rec- 

 ords of the several glacial epochs on the 

 north slope of the Alps. 



THE ORIGIN OV LAKE ZURICH. 



The j)roblem of Lake Zurich is presented 

 in a masterful manner by Aeppli in the 

 thirty-fourth number of the Beitnige zur 

 Geologhchen Karte der Schiveiz, in brief as 

 follows : The valley of the Linnnat. in which 

 the lake lies, was eroded in broad upland 

 over wliich the Declcemchothf of the first 

 glacial epoch had been previously spread. 

 That the erosion of the valley was performed 

 in the normal fashion by weather and water, 

 and not by ice, is shown by the graded ter- 

 races or rock benches, traceable more or 

 less continuously along its sides : these ter- 

 races being independent of rock structure, 

 and associated with similar terraces in 

 other valleys, all leading agreeably to the 

 conclusion that after the first glacial epoch 

 the region was generally elevated and the 

 streams thereby given increased power of 

 erosion. The Deekeuschotter. where preserved 

 on the ridges between the adjacent valleys, 

 together with the terraces ou the valley 

 slopes, are bent tjackwards across a belt six 



