Correspondence—Sir H. H. Howorth. 89 
The necessity for the narrow 20 million years’ margin, which 
clashes with geology, is seen then apparently not to have the slightest 
foundation. It rests on the gratuitous hypothesis that the sun’s heat 
was derived solely from gravitation, entailing an approach of matter 
in a primitive state of repose. The quantity of heat generated under 
these premises was calculated originally by Helmholtz to suffice for 
20 million years of solar radiation. 
Moreover, the sun is not yet cooled down: so that a notable part 
of the 20 million years period, which is the inexorable limit of the 
above hypothesis, must be spread over fuéwre time. How much is 
left for past duration of the solar system and for geological history 
of our globe then? Neptune and Jupiter were certainly shed from 
the revolving-contracting solar nebula some millions of years before 
the Earth, i.e. before the Earth had a separate existence. Some 
millions of years must be then inevitably lopped off the other end 
of our already contracted time-margin. What is left over for the 
Harth’s past existence then: so that on the (exclusive) gravitational 
hypothesis of the source of the sun’s heat, no geological epoch 
worthy of that name would remain. S. Totver Preston. 
Hampura, Dec. 14, 1892. 
THE MOMMOTH AND THE GLACIAL DRIFT. 
Srr,—I wish Mr. Jukes-Browne had devoted a little more of his 
last letter to Geology and a little less to offensive personalities. To 
these latter I do not propose to reply. What is alone interesting to 
your readers in this correspondence is to fix the exact age of the 
Mammoth, a matter of importance not only to the geologist but more 
especially to those devoted to the early history of man. To the 
settlement of this problem Mr. Jukes-Browne’s last letter adds 
nothing. He reverts to two cases he had already quoted, one of them 
the well-known case at Hoxne, where, as I showed, there is not only 
no positive evidence forthcoming but which was riddled through 
and through by Mr. Flower. There can be no doubt whatever that 
judging by the published evidence the case of Hoxne breaks down. 
There is some evidence that at that place the drift beds overlie the 
Mammoth bed. There is none that will bear criticism that they 
underlie it. 
The second case from Burgh, where it was not the Mammoth but 
the Hlephas antiquus that was found, I have already criticized. 
I must correct a curious delusion of Mr. Jukes-Browne, that on 
this question I have set myself against the best authorities. The 
best English authorities on the age of the Mammoth known to me 
are Professor Dawkins, Professor Geikie and Dr. Hicks,! all of whom 
virtually agree with me, or rather, I with them. The French 
geologists are almost without exception on the same side, while 
among the geological surveyors, to whom perhaps Mr. Jukes-Browne 
limits “authority,” Mr. Lamplugh and Mr. Skertchly have been 
liberally quoted by myself, but as a mattor of fact authority has and 
ought to have very little place in geology any more than in any 
1 See Dr. Hicks’s letter.—Epir. Grou. Maca. 
