382 Murchison’s Siluria. 
is another important fact which seems to us to indicate that the. 
conditions for the growth of organic life in that part of the earth. 
were unfavorable during the earlier periods of animal and veget- 
able existence. If the internal heat of the earth be adopted, as. 
is done by most geologists, as the principal cause of the more uni-. 
form and elevated temperature of the globe during the earlier 
geological periods, is it not a legitimate inference to conclude that 
the same causes which rendered the now frozen arctic zone sufli- 
ciently warm to support a prolific growth of plants and animals, 
must have so increased the temperature of the equatorial regions 
that life could not exist there except under peculiar an ce 
tional circumstances? Thus, the colder portions of the earth are 
by far the best provided with coal, and within the limits of the 
torrid zone there seems to be almost a total want of the proper 
coal-measures, — 
. The order of the paleontological development of the paleozoic 
strata can nowhere be so well studied as in North America. The 
vast space over which the older fossiliferous rocks are spread out 
and the fact that, in spite of the immense period since the ani- 
_ mals and plants entombed in them lived and flourished, they re- 
main almost in the same position in which they were originally 
deposited, are two strong reasons why this study should be car- 
ried on in this country with vigor and success. he labors of 
James Hall have already shed a flood of light over this, the most 
interesting, department of our geology, and we look on the vol- 
umes of the “ Paleontology of New York” as a not less import- 
ant contribution to our knowledge of the paleozoic world than 
those of Murchison or Barrande. Much yet remains to be done 
in our great western valley, before our acquaintance with the his- 
tory of the development of organic life in our older strata will 
have reached anything like a satisfactory stage. When the various 
groups, which have been so. thoroughly studied in New York by 
Hall, shall have been equally well worked out in their western 
and southwestern extension, we shall have a more complete pic- 
ture of palzozoic life, as developed under every variety of physi- 
cal condition, than any part of Europe can furnish. Thanks to 
the labors of Mr. Logan in Canada, we are fast gaining a knowl- 
edge of that interesting region thus getting a clue to some of the 
intricacies of New England geology, so that we may hope that so 
large a part of our northeastern states will not always remain but 
little better than a blank upon our geological maps. . ra 
- The subject of the original formation and distribution of gold 
over the earth’s surface is one in which Murchison has, since 4! 
visit to the Ural, been particularly interested, and a chapter of the 
—— devoted to a recapitulation of what he has or 
ublished in regard to it. In 1844 our author was led, priv 
cipally by an examination of specimens collected by Count 
Rf 
