190 Correspondence—Ur. S. V. Wood, jun.—Rev. E. Hill. 
my feeble powers of comprehension that all I can do is reverentially to 
take off my hat to these several gentlemen, and subside; maintaining, 
nevertheless, that the delineation given by Mr. Harmer and myself in 
1871 of the beds of the Cromer Cliff is (subject to the clearing up of 
what may be involved in the unconformity in the midst of the Lower 
Glacial of the cliff at Hasborough, and eastwards of that place, to which 
we called attention by sections and remarks) quite correct, Mr. Reid’s 
many subdivisions notwithstanding ; as is also the age and position of 
the beds of the Cromer Cliff section, relatively to the chalky clay that 
we assigned to them. As regards the mode in which the morainic clay 
was laid over the sand, I have in a paper sent in to the Geological 
Society, and now awaiting its turn for reading, given my view. 
Szartes V. Woop, jun. 
DR. CROLL’S ECCENTRICITY THEORY. 
S1zr,—May I be allowed to suggest to Dr. Croll that he should offer 
some explanation how the glaciation of North America, as compared 
with that of Europe, is to be reconciled with his theory. ‘Ihe dif- 
ference between the Kastern side of North America and that of the 
west of Europe is admitted to be the result of the ocean currents now 
existing; but the glaciation of the two regions was merely an equal 
increase of the cold in both, without change in their relative propor- 
tions; the same differences which now exist being shown by the limit 
to which glacial evidences extend in both regions to have obtained 
during that glaciation. 
This, as I have on more than one occasion observed, appears to me 
to be a conclusive objection to Dr. Croll’s theory, which he admits to 
be baseless unless there were a complete diversion of the warm ocean 
currents from the hemisphere glaciated; and its satisfactory removal 
would to my mind be worth any amount of those subtle reasonings on 
the physics of heat in which Dr. Croll is so fertile, but which seem to 
me to be obnoxious to the reproach often levelled at figures, viz. that 
they may be made to prove anything. SEearLes V. Woop, jun. 
ECCENTRICITY AND GLACIAL EPOCHS. 
Srr,—Dr. Croll in his article in February last speaks of an erroneous 
assumption, that if the annual receipt of heat be far more than suffi- 
cient to melt the annual snow-fall, then such snow must be melted. 
He does not point out wherein the error lies, and I feel very doubt- 
ful whether I understand what he is referring to. The assumption, 
he says, is totally opposed to the known facts of Greenland. This 
statement seems rather too strong. He quotes Meech’s calculation 
that the heat received there, neglecting that cut off by the atmosphere, 
is enough to meit 50 feet of ice. We must make allowance for the 
great thickness of air traversed by the sun’s rays, and for the loss of 
heat by the great obliquity of reflexion. A very rude calculation, with 
no pretence to accuracy, brings out that these reduce the heat received 
by the ground, to sufficient for melting only some 16 feet of ice. 
Since to vaporize ice requires 7} times as much heat as to melt it, 
this would dissipate by evaporation only little more than two feet 
