GEOLOGY OF THE VALLEY. 297 



riiie shells;* .the supposed bearing of which, upon the 

 interpretation of the geologic facts of the Amazonian 

 Valley, has been made known by Prof. Orton. There is 

 here an interesting qiiestion relative to intertropical gla- 

 cial phenomena. Prof. Agassiz, after careful and extended 

 examination of the deposits, concludes that an ancient gla- 

 cier once ploughed through the Amazonian Valley. From 

 the report of a paper on the valley of the Amazons, read 

 August 20, 1870, by Prof. Orton, before the American 

 Association for the Advancement of Science, we quote the 

 following : " The conclusion reached was that facts were 

 incompatible v/ith the existence of an equatorial glacier, 

 and even of an intertropical cold epoch." Setting aside 

 all generalizations, let us look at naked facts — see what 

 evidences of glacial action have been found in these tropi- 

 cal regions. 



The geologic formations of the Amazonian Valley have 

 been carefully studied by Agassiz, and are given by him 

 as, first, a coarse arenaceous material, resting upon a cre- 

 taceous formation, indications of which appear about the 

 edge of the valley ; then a deposit of finely-laminated 

 clays, overlaid by sandstone, fully eight hundred feet in 

 thickness. This has been subjected to denuding agencies, 

 which, toward the lower portion of the valley, have re- 

 moved, in some instances, the entire thickness of the de- 

 posit, leaving isolated, flat-topped mountains, such as the 

 liills of Almeyrini, vrhich form the most consj^icuous ob- 



* ilr. Conrad, to whom these shells were submitted for identification, 

 gives the number of species as seventeen, all extinct, belonging to nine 

 genera, only three of which are now represented. The following list 

 contains the most important ; others may yet be added : Isaca Ortoni, I. 

 Lintea, Liris laqueta, Ebora crassllabra, E. bella, Ilemisinus sulcatus, 

 Dyris gracilis, Neritina Ortoni, Bulimus linteus, Pachydon (Anisothyris) 

 tenuis, P. carmatus, P. oblicjuus, P. crcctns, P. cuncatus, P. ovatus, P. 

 altus, and a bivalve allied to Mulleria. 



