7? a 
a 
Review of Recent Geological Literature. 255 
railway. It describes the early mining and attempts at mining in 
Montana, mentions many stirring incidents of early discovery and set 
tlement, illustrated by many scenes of natural topography and ‘erosion, 
mountains, valleys and gorges. Its excellent and numerous half-tones 
are in the best style and the typography and printing are without blem- 
ish. It also embraces short descriptions of the Yellowstone Park and 
of the Puget Sound country. Its author is O. D, Wheeler. It is 
printed for general distribution, and can be obtained by sending six 
cents in postage stamps to C. S. Fee, St. Paul, giving address. 
N. H. W 
The Chronological Distribution of the Elasmobranchs by O. P. Hay, 
(Am. Phil. Trans. vol. 20), 
In a paper in Science for 1899 the author published a diagram which 
was intended to illustrate the chronological distribution of the fossil 
fishes of North America. The present paper is an elaboration of the 
same subject, in a consideration of the single group—the sharks—in both 
North America and Europe. The results show that the group under- 
went two culminations, one in Sub-Carboniferous, the other in early 
Mesozoic time, and that although there were slight variations in number 
- in the two localities, as a general rule the rise and decline of the group 
was contemporaneous in Europe and America. At the close of the 
Permian there. was an almost complete extinction in both localities. 
From the Miocene to the present there has been a decline. Dr. Hay 
plots these facts upon a curve. The curve can be taken as relatively 
accurate only, since no account is taken of the varying conditions of 
fossilization prevailing in these different ages. The sharks, being 
pre-eminently cartilaginous, are particularly in need of the best con- 
ditions of fossilization. 
A consideration of the various families of elasmobranchs brings 
out some interesting facts. Starting with the generalized stem of 
which Cladoselache fs the nearest known representative, various branch- 
es were given off which culminated in the adaptive forms of the Sub- 
carboniferous. The second culmination is conclusively shown not to 
be a return of these same specialized forms, but is a second radiation 
from a generalized stem. Only one family survived the break between 
Palaeozoic and post-Palaeozic time. This is the family represented 
by Cestracion, the present Port Jackson shark, and this family can be 
traced back to the Devonian, and represents an outgrowth of the 
Cladoselachian line and hence the stem line of both radiations. 
These facts are most interesting, and Dr. Hay is to be congratu- 
lated upon the careful work he is doing. He offers no explanation 
of the facts beyond a rather unsatisfactory suggestion of a loss in 
vital force from over specialization as a cause of the Permian extinction. 
Since the development of the family took place for the most part tn 
continental seas which were uplifted and became dry land with the Ap- 
palachian revolution, it hardly seems surprising that highly specialized 
