’ 
Correspondence—Mr. W. H. Daiton—Mr. N. Taylor. 333 
a fixed amount of heat we have double the work to do in reconvert- 
ing this snow into water and vapour. Hence, we must conclude 
that the available heat influencing the climate is decreased by 
exactly the amount expended in this work, and therefore a con- 
tinuance of the greater snowfall must have the effect of lowering 
the average temperature of the climate. 
On page 17 of your January Number, Mr. Hill argues that owing 
to increased radiation being greater in proportion to the increase of 
temperature, therefore, that this may be a cause of glaciation. He 
apparently ignores the fact that if radiation is increased in greater 
proportion by a rise in the temperature, it is decreased in like pro- 
portion by a fall, and that therefore the total annual radiation with 
a fixed amount of heat received is therefore also a fixed amount. 
If this total radiation was not a fixed amount, would it not have the 
effect in high latitudes, where there is a great difference in quantity 
of heat received between summer and winter, of causing a Glacial 
Epoch? And if so, how is it that with this cause of glaciation 
the action does not spread towards the equator as it should do if so 
caused? * Jos. GREENWOOD. 
Dunuam, June ist, 1880. 
“ POST-GLACIAL.” 
Srr,—Might I ask the anonymous reviewer of my pamphlet 
memoir on the Colchester District! to state in what esoteric sense he 
uses the word Post-Glacial; at what point in the northward reces- 
sion of Arctic conditions he draws the chronological line between 
the Glacial and Post-Glacial epochs; and why he supposes that 
those conditions obtained outside of the Arctic Circle at the time of 
formation of the beds I have described as Post-Glacial in the work 
in question. 
The mammalia and most of the invertebrata are present in the 
middle and lower terraces of the Thames Valley, whilst Unio 
' littoralis, three of the Helices, and several of the Coleoptera indicate 
the climate of more southern latitudes, and Corbicula fluminalis is a 
sub-tropical species. 
Further deposits have been formed under the existing geographical 
conditions as valley brickearths and foreshore mud and sand, up- 
heaval of the latter to about 30 feet having taken place, with an 
equal extent of deepening of the valleys in consequence. 
Harweston, 13th June, 1880. W. H. Datrton. 
1 Grou. Maa. June, 1880, p. 2 
THE CUDGEGONG DIAMOND FIELD. 
Mr. Norman Taylor, whose paper, bearing the above title, was 
published in the Grotocican Macazing, 1879, Vol. IX. pp. 399-412, 
and pp. 444-458, requests permission to make the subjoined correc- 
tions, viz. :— 
