Searles V. Wood—The Cause of the Glacial Period. 293 
attached by one end to the crystalline walls, while the other end is 
directed towards the central parts of the inclusion. 
In among the larger crystals are many smaller ones, especially of 
felspar. 
The residual glass which binds the other constituents together is 
filled with the same hair-like microliths mentioned as occurring in 
the glass inclusions in the felspars, and in some parts they show 
fluidal structure. The glass fuses in the Bunsen burner with con- 
siderable intumescence. 
On the whole, the rock is very similar to some of the hornblende 
andesites of the Philippine Islands described by Oebbeke in the 
Neues Jahrbuch, Beilage Band I. 1881, but with the exception 
that the accompanying pleochroic pyroxene is rhombic instead of 
monoclinic, hypersthene instead of augite. 
74, GoucH Roap, BrrMincHaM.. 
Til.—On tHe Cause oF THE GLACIAL PERIOD. 
By Szarxes V. Woop, F.G.S. 
N concluding an article on ‘“‘The Climate Controversy” in the 
Geo. Maa. for September and October, 1876, I observed (p. 451) 
that it had long appeared to me that the ‘Glacial period proper” 
was due neither to a change in the earth’s axis, nor to any variation 
in the eccentricity of the earth’s orbit, nor to any changes in the 
distribution of land and water, but to a diminution in the heat-emit- 
ting power of the sun. In a memoir on the Newer Pliocene period 
in England, published in the Quarterly Journal of the Geological 
Society for Nov. 1880, and Nov. 1882, wherein I have endeavoured 
to trace in detail the succession of events in this country from the 
commencement of the Red Crag down to the close of the Minor 
Glaciation, I have reiterated that view, as being the only one that is 
reconcileable with the succession thus traced; for with the exception 
of the single interval of warmer climate in which the beds termed 
by me the “ Cyrena fluminalis formation” accumulated, and which 
was succeeded by the renewed refrigeration that I have termed the 
“Minor Glaciation,” and regarded as coincident with the second 
advance of the Alpine glaciers long ago detected by Continental 
geologists, I have not been able to discover any indication of those 
alternations of warm and cold climate, which form an indispensable 
part of the eccentricity theories of Adhemar, Croll, Murphy and 
others. i 
In the case of North America, there has also been a failure 
altogether, on the part of the geologists of that country, to detect 
evidence of more than one alternation of climate during the Glacial 
period; and this one seems to be precisely that to which I have 
referred.* 
1 For evidence of this single alternation in the States of Iowa and Illinois, see 
McGee in Amer. Journ. of Sci. 8rd series, vol. xv. p. 241; in Nebraska, see 
Hayden’s Report on the superficial deposits of Nebraska for 1874; and in British 
Columbia, see G. M. Dawson in Q. J. G. 8. vol. xxiv. p. 122. G.K. Gilbert (of the 
