94 
Correspondence — Mr. Alfred R. C. Selwyn. 
As the object of the paper was to arrange facts rather tlian 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 Oxford 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. 
COEBBSPOlTDElirCE. 
ORIGIN 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 thern 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, Georgia, 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 irregulär in its action, and that offen 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 roch 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 of Canada, Alfred B. C. Selwyn. 
Montreal, D ec. 20 , 1876 . 
MR. DURHAM ON KAMES, AND MR. MELLARD READE ON 
BOULDER-CLAY. 
g IRj — If Mr. Durham’s Karnes 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 swamp- 
