238 The American Geologist. April, 1892 
anterior margin, at the point of the lateral angulation, backward 
to the median line, at about half the length of the carapace, form- 
ing a large V-shaped depressed area over this part of the surface. 
The ornamentation has been only pustules and pits on the cara- 
pace and segments. 
This specimen is said by Dr. A. 8. Tiffany to have been found 
in the Kinderhook group at Kaskade, three miles west from the 
court house at Burlington, Iowa, in a forty foot bed of clay shale 
containing many nodules or concretions, one of which this has 
occupied. The type example of the genus and species above men- 
tioned was found in a concretion, from the Krie shale at Leroy, 
Lake Co., Ohio, which is probably of the horizon of the Chemung 
group of New York, though this is not entirely settled. 
PHYSICS OF MOUNTAIN BUILDING; SOME FU N- 
DAMENTAL CONCEPTIONS. 
T. MELLARD Reave, CE. F. G. 8., Park Corner, Blundellsands, Eng. 
One of the most frequently urged objections against the theory of 
mountain evolution with which my name is associated™ is its sup- 
posed inadequacy to the production of the requisite lateral pres- 
sure. [hope to be able to show that much of this criticism is 
founded upon misapprehension; that it in fact gives more play in 
this direction than any other theory consistent with geological 
facts, at present in the field. ; 
The fundamental idea underlying all these theories, and there 
are really very few of them, is that our globe is a cooling spheroid. 
It arises from this, that orographie changes can only occur from 
actual loss of heat by a part of the spheroid, or by redistribution 
of heat and pressure relative or absolute. These principles will 
become more obvious as we proceed in our inquiry. 
Changes directly brought about by actual loss of heat, or what 
is called secular cooling, have formed the basis of a theory that 
has held the field for a very long time, and when we do not in- 
quire too closely into the reasoning upon which it is founded, or 
indulge in quantitative investigation, it meets some of the first 
« prior’ Conceptions of the sort of an agent required to effect the 
gigantic corrugations seen insome of the world’s mountain chains. 
It has the merit of being a simple idea easily grasped, and the 
“Origin of Mountain Ranges. 
