Correspondence — Mr. J. Gumi. 47 



only, as I expressly stated, in so far as it coincides with Prof. Dana's 

 theory. Granting the probable validity of Prof. Le Conte's first 

 objection, that the coefficient of contraction is probably not the 

 same in parts of the earth differing in composition, it simply shows 

 that his theory is not so different from Prof. Dana's as I had 

 su})posed ; although he still locates the Continents where Prof. Dana 

 locates the ocean-floors, and demands a globe continuously rigid from 

 centre to circumference, which Professor Dana does not. 



Prof. Le Conte says that, unless we assume that the earth is 

 preternaturally homogeneous, the very slight deformation exhibited 

 by its surface would result from cooling. This appears to be a 

 sufficient answer to my argument, so far as it applies to Prof. Le 

 Conte's own theory, since he says the inequalities of the surface are 

 due to unequal contraction of the radii through their entire length. 

 But Prof. Le Conte's criticism does not meet my argument in its 

 application to Prof. Dana's theory ; for Prof. Dana says the oceanic 

 hollows are due to the unequal contraction, not of 4000 miles of 

 earth-matter, but of only about forty miles. His theory supposes 

 that the earth has a thin solid crust, separated by a mobile layer 

 from an immense solid nucleus, and that the inequalities of the 

 surface are due to unequal contraction of this thin external crust 

 alone. Hence Prof. Le Conte's illustration should be modified. 

 Instead of taking a ball of molten iron or rock as a model of the 

 whole earth, suppose a layer of molten iron or rock to represent the 

 earth's crust. Let this layer be forty inches thick ; then Prof. Dana 

 says that when the whole is solid the layer will be three inches 

 thicker in some parts than in others, in consequence of unequal 

 contraction. Now I claim that this unequal conductivity and con- 

 traction, amounting to about eight per cent., requires, in the case of 

 the earth, an unproved and improbable difference in composition. 



If Prof. Le Conte will consult the last published expression of 

 Prof. Dana's views (Amer. Journ. of Science, 3, vi. p. 168), he will 

 find that Prof. Dana does hold that the steep slopes of the oceanic 

 depressions are due to the supposed original difference in composition 

 and conductivity of the continental and oceanic areas. I have not 

 ascribed this view to Prof. Le Conte, but he seems to have both 

 misread and misquoted me here. 



Finally, although I have taken account only of the contraction 

 due to solidification, yet I think this is fair, because I have made (he 

 extremely favourable supposition for Prof. Dana's theory that the 

 oceanic areas remained liquid until the continents became entirely solid. 



Boston Society of Natural History, W. 0. Crosby. 



Boston, U.S.A. 



THE MAMMOTH IN THE FOEEST-BED. 



Sir, — By a singular coincidence, the day after I received a copy 



of my paper on the occurrence of the Mammoth in the Forest-bed , 



a heavy storm laid bare that bed at Overstrand and Sidestrand. I 



took the first opportunity to go to Cromer, and Mr. Alfred Savin 



