524 Correspondence—Mr. S. B. J. Skertchly. 
metal such as iron or copper turned to a true spherical form while 
red-hot and allowed to cool, would deform more than that amount. 
Is not the burden of proof, then, on the other side? Ought not 
the objector to show cause why he assumes so preternatural a 
homogeneity ? 
3. But says Mr. Crosby, p. 244, “If we admit that the earth is of 
different composition on different sides, it would certainly be con- 
trary to all analogy to suppose that the areas of different composition 
are sharply marked off from each other. Yet the steep slopes of 
oceanic depressions require according to these theories an abrupt 
change in radial contraction.” 
I would remind Mr. Crosby that according to my view (and also 
to Prof. Dana’s) this steep slope of oceanic basins is due to mountain- 
making not continent-making causes. 
4, In making some estimates of the amount of contraction, p. 244, 
Mr. Crosby takes account only of the contraction by solidification. 
But manifestly this is only a part, and perhaps but a small part of 
the whole contraction by cooling ; and in addition to this there may 
be other causes of contraction besides cooling. . 
There are several other points which I might notice, but I fear it 
would make this letter too long. 
BERKELEY, CatirorniA, U.S.A. 
JosEPH L&E Contre. 
THE PERMANENCE OF OCEANIC AND CONTINENTAL AREAS. 
Str,—As a believer in and advocate of the “hypothesis of the 
permanence of oceanic and continental areas” now “ becoming 
fashionable,” and in the course of many years’ daily work among 
rocks never having seen or heard of an actual case of a true “ deep- 
sea” deposit, I should like to make a few remarks on Mr. Mellard 
Reade’s paper on the “ Age of the Earth.” 
First, I fail to see the slightest connexion between the area of 
exposed igneous rocks and the number of times sedimentary beds 
have been ‘worked over” again. Surely at the beginning of 
geological time all the land was igneous, and practically that area 
has been diminishing ever since. This can therefore afford no clue 
to the question. 
Secondly, as to the maximum thickness of rocks, which is what 
Mr. Wallace deals with, the tendency is rather to overestimate than 
underrate it. For example, it is usual to estimate the thickness of 
the Cretaceous rocks by adding together the maximum thicknesses in 
different localities, but this gives quite an erroneous result, and if 
applied to West Norfolk would make the result too great by about 
2700 feet. In other words, 2800 feet of rock in various other 
localities were formed while only 100 feet were deposited in Hast 
Anglia. Jam not taking account of beds removed by denudation ; 
for there is no proof that the Maestricht beds, Upper Greensand, 
Gault, or Wealden ever existed there, and the Neocomian is under 
100 feet. But to add together all these beds and take the sum as 
indicating the time of deposition, is as incorrect as it would be to 
