1897.] Geology and Paleontology. 223 
Queries on Rock Differentiation.—The theory of the differen- 
tiation of rock magmas,now so generally held by lithologists,is questioned 
by Mr. G.F. Becker. The following is an abstract of his discussion of 
the subject : 
“All known processes by which the segregation or differentiation of 
a fluid magma could take place involve molecular flow. This is demon- 
strably an excessively slow process, excepting for distances not exceed- 
ing a few centimeters. Soret’s method, even if it were not too slow, 
seems inapplicable, because it involves a temperature unaccountably 
decreasing with depth. The normal variation of temperature, an in- 
crease with distance from the surface, would be fatal to such segregation. 
The least objectionable method of segregation would be the separation 
of a magma into immiscible fractions ; but this seems to involve a super- 
heated, very fluid magma, while the law of fusion and the distribution 
of phenocrysts in rocks indicate that magmas prior to eruption are not 
superheated to any considerable extent, and are very viscous. 
“The homogeneity of vast subterranean masses called for by the 
hypothesis of differentiation is unproved and improbable. The differ- 
ences between well-detined rock types are more probably due to original 
and persistent heterogeneity in the composition of the globe. Hypogeal 
fusion and eruption tend rather to mingling than to segregation, and 
transitional rock varieties are not improbably mere fortuitous mixtures 
of the diverse primitive, relatively small masses of which the lithoid 
shell of the earth was built up.” (Amer. Journ. Sci., 1890.) 
The Coal Measures of Arkansas.—The descriptions of marine 
fossils from the Coal Measures of Arkansas, by Mr. J. P. Smith, are of 
especial interest, since they afford means of correlating strata of differ- 
ent regions, and also because marine fossils are usually rare in the Coal 
Measures, Among the important finds are two species of Pronorites, 
to which the writer refers as follows: ares 
“ The finding of Pronorites in Arkansas is of great importance, since 
it is the ancestor of a form, Medlicottia, which, though unknown in 
Arkansas, has been found at no great distance, in the Texas Permian. 
These occurrences help to prové the continuity of life from the Car- 
boniferous into the Permian, and to show that the same conditions 
existed here as in the Artinsk region of the Ural Mountains, where the 
Carboniferous beds contain the goniatites, out of which most of the 
Permian ammonites were developed.” 
— The relations of the strata in which these fossils were found to the 
Coal Measures in both the Old World and the New is shown in a cor- 
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