Revievj of Recent Geological Literature. 313 
of Colorado are underlaid with coal. Texas has 30,000 sq. miles, Da- 
kota 100,000 sq. miles. New Mexico has at least 600,000 acres of coal, 
ranging from anthracite to lignite, "Wyoming 20,000 sq. miles, Montana 
20,000 sq. miles." 
Judging from the analyses, many of which are given in the volume, 
most of these coals are of good qualitj^, standing low in moisture and in 
sulphur and not excessively high in ash. Doubtless only the best 
seams and the best parts of them will at present pay for working. 
Prof. Lakes points out that the anthracite though of good quality is 
not known to be sufficient in quantity to make it a factor of impor- 
tance in the resources of the State. 
The volume is well illustrated with fifteen outline views which aid 
largely in enabling the reader to follow and understand the nature 
of the country and its geology. 
The Eoolutlon of Climate. By James Geikie, LL.D., F.R.S. pp. 22 ; 
with maps. (Reprinted from the Scottish Geographical Magazine for 
Feb. 1S90.) This paper will be of much interest and value to students 
of paheontology and of structural and glacial geology. It is accom- 
panied by two plates, the first of which shows four small sketch-maps 
illustrating the geographical evolution of continental areas, and the 
second is a geological map of the world by J. G. Bartholomew. 
The early origin and permanence of the continental jilateaus and 
oceanic basins is maintained, as taught by Dana ; but during Archfean, 
Pahieozoic and Mesozoic time the present extensive land areas were 
probably represented by islands, between which shallow expanses of 
sea permitted marine currents to carry warmth from the tropics to the 
circumpolar regions. These conditions produced very remarkable uni- 
formity of climate, and consequent close relationship of the fauna and 
flora, over the whole glol)e. In the Cainozoic era the extent of the 
land increased, causing the sea to retreat from hitherto submerged 
parts of the continental plateaus ; and the land-growth was attended 
by a gradual lowering of the temperature of northern and temperate 
latitudes and the differentiation of climate into zones. 
We now come to the principal purpose of this paper, which is a de- 
fense of Dr. Croll's theory of the causes of the ice-age. Professor 
Geikie believes, with Wallace, that extensive ice-sheets, like those of 
the Quaternary glacial period, could not be formed in earlier eras be- 
cause the influence of recurring epochs of maximum eccentricity of the 
earth's orbit was then mainly counteracted by the geographical con" 
ditions, with a possible exception in the Permian period. His adher' 
ence to this astronomic theor)' seems not to have taken account of 
recent investigations by geologists in this country, who are led to 
measurements of postglacial time, from the recession of the falls of 
Niagara and Saint Anthony, and from the rate of wave-erosion on lake 
Michigan and the resulting formation of deposits of beach sand and 
dunes, which show that the departure of the ice-sheet of the last 
glacial epoch in the northern United States was only some 7,000 to 
