NOTES ON GEOLOGY. 427 



premises is proved, especially by osteological relics. M. Liais 

 enters into the glacial theory at great length, but I must refer my 

 readers to his book for a full consideration of the subject. He 

 holds that so far from the equatorial region being less warm at 

 any past epoch, the temperature must have been higher to permit 

 the formation of the vast amount of vapour necessary to produce 

 the snows and ice in the temperate zone, which brought about 

 our glacial period. Besides which, no rotation of the earth's axis 

 could make the equatorial region even temporarily polar. M. 

 Liais also cites the existence of remains of animals in the caves 

 covered by the same red clay which M. Agassiz considers to be 

 drift. These animals must have lived prior to the supposed glacial 

 epoch, yet they are identical with existing species now found in 

 the same localities. 



M. Liais also shows that the so-called erratic blocks are in 

 close proximity to the virgin rock whence they have b een derived. 

 This is also the case with the angulated quartz pebbles described 

 by Mr. Hartt as water-carried stones lying under the drift clay ; 

 dykes and veins of the same material are always in close proximity. 

 M. Liais says, "When one is assured that these blocks come 

 really from the region where they are met with ; when one sees 

 them sometimes still partially fixed in the decomposed gneiss with 

 its primitive stratification " (as I have described on the Corcovado 

 and Petropolis Railways) ; " when, finally, one observes the vast 

 scale on which the decomposition of rocks by atmospheric action 

 is carried on in Brazil; — these phenomena have a simple and natural 

 explanation, excluding entirely the idea of transport." The 

 rounded forms which some of these blocks present is also attribu- 

 table to atmospheric action. M. Agassiz even describes rocks tn 

 situ with the same pecuUarities. 



It is very difficult to estimate the thickness of the gneiss for- 

 mation in Brazil. In the Corcovado range, M. Liais estimates 

 it at a thousand metres. In the Organ Mountains and the 

 Mantiquiera range, in the province of Rio de Janeiro and South 

 Minas Geraes, at six thousand metres. 



