﻿94 Correspondence — Mr. Alfred R. C. Sehvyn. 



As the object of the paper was to arrange facts rather than to 

 propound theories, the conclusion was chiefly occupied in summing 

 up and correlating. It was shown that, since the leading feature 

 of the rock masses between the Oxfoi-d and Kimmeridge Clays is 

 variety, a strict and rigid correlation is altogether impossible. Yet, 

 in spite of great local differences, producing in many places a 

 strongly contrasted facies, there are certain features which may be 

 deemed fairly characteristic of the several divisions. The bank-like 

 character of most of these beds was insisted upon. A table of com- 

 parative sections, 14 in number, affording a generalized idea of the 

 development, was exhibited, and the stratigraphical verifications of 

 many of these given, as sections drawn to scale, in the body of the 

 paper. 



coi2,i^:Es:F'Oisri:):E3^o:E. 



OEIGIN OF LAKE-BASINS. 



Sir, — In reading the correspondence and remarks on the origin of 

 Lake-basins in the November Number of the Geological Magazine, 

 it has occurred to me that the glacial origin of these basins may be 

 explained without supposing the ice to have scooped them out of 

 solid rocks such as we now see around them. I have been led to 

 this idea by a study of the phenomena connected with the decom- 

 position of rock in situ in southern latitudes — Australia and Brazil. 

 Similar facts may likewise be seen in South Carolina, G-eorgia, etc. 



In these regions, which have never been glaciated, the surfaces 

 over more or less extensive areas consist of quite soft decomposed 

 rock, and mining operations have shown that this decomposition 

 has been very irregular in its action, and that often great masses, 

 resembling boulders, are quite unchanged, though completely sur- 

 rounded by the decomposed material ; and the varying depth to 

 which the decomposition has extended has resulted in producing a 

 solid rock surface as full of hollows and depressions of all shapes 

 and sizes as can be found in any of our northern lake regions. And 

 if we admit that prior to the Glacial period these northern lake 

 regions were similarly covered with decomposed rock, then the ice 

 would not be called upon to exert any very extraordinary power in 

 order to scoop out any number of lake-basins, and to leave enormous 

 boulders scattered over the face of the country as we now find them. 



Geological Survey or Canada, Alfred E. C Selwyn. 



Montreal, Dec. 20, 1876. 



ME. DUEHAM ON KAMES, AND ME. MELLAED EEADE ON 

 BOULDEE-CLAT. 

 gi^^ — If Mr. Durham's Kames be the equivalent of the English 

 and Irish Eskers, I cannot help thinking that he has not had 

 an opportunity of seeing a series of good typical sections of 

 these deposits. Along the east borders of North Wales (where 

 I have examined the Eskers) clear sections demonstrate that 

 their surface-configuration has been scarcely at all altered by at- 

 mospheric action, and that the internal structure of the swampr 



