102 J. D. Dana—Notice of Hunt's Essays. 
Art. XII.—Notice of the Chemical and Geological Essays of T. 8. 
Hunt ;* by James D. Dana. 
Mr. Hunt has brought together, in this volume of Essays, 
various memoirs which have been published by him in this 
Journal and elsewhere. The chemical papers are important 
contributions to science, and show that the author was among 
the first to appreciate the principles which lie at the basis of 
what is called modern chemistry. He further applied the prin- 
ciples to the department of mineralogy; and in the view 
which he presented in 1859 with regard to the molecular rela- 
tions of the feldspars, he appears to have anticipated Tschermak 
y ten years. e chapters on chemical geology contain much 
that is valuable, though not all original, on the origin of igne- 
ous and metamorphic rocks, of dolomite and gypsum, of vol- 
canoes, of mountains, and on other topics, yet coupled with 
opinions, of fundamental importance, especially with reference 
to the making of mountains, metamorphism and the origin of 
some kinds of rocks, which science, we think, will never sus- 
tain. There is an important chapter on “Bitumen and Pyro- 
schists,” + pointing out the relations in chemical constitution 
between mineral oil and certain vegetable and animal tissues, 
ar 
as the fauna and stratification go, there is the closest relation 
ing beds 
The reader of the volume will observe that in the Third® 
Chapter the White Mountain series and Green Mountain series 
of rocks are made (as had been done by other geologists) Lower 
Silurian, and Upper Silurian and Devonian, in age, while in the 
Thirteenth Chapter (as also mentioned in the preface to Chap- 
view, as I believe I have proved, is the one sustained by the 
facts. The new view is wholly speculative, being based on no 
careful stratigraphical study of the regions, but mainly upon 
the assumption that certain kinds of crystalline rocks are a test 
of geological age the world over. Since the first announcement 
of this doctrine by Mr. Hunt, I have spent many months in the 
* Chemical and Geological Essays, By Thomas Sterry Hunt, LL.D. 490 pp. 
8vo. Boston. 1875. (James R. Osgood & Co.) 
+ Mr. Hunt’s convenient term “ pyroschists,” applied to shales containing car- 
bonaceous material, is objectionable in that the rocks are shales and not schists; 
and on this account I have not adopted it in my Geology. 
