‘188 Geological Results of the Earth’s Contraction. 
contraction in progress. Facts on record prove farther, that these 
grand catastrophes had their widest influence after the coal era, 
and became less and less general’as succeeding ages rolled on. 
IX. These principles give us some data for comparing the 
energy of forces in. past times in the earth’s history, with those 
ing, we may be considered as proceeding on an hypothetical basis. 
Yet in reasoning without reference to them, is the ground assum 
any the less hypothetical ? With those who believe in the former 
igneous fluidity of our globe, contraction is the grand and fun- 
damental agency to be first considered after the general principles 
of solidification. ae 
X. Tides and parorysmal movements beneath the crust of the 
globe.—In the course of this article we have not alluded to the 
effects of tidal and’ other motions in the heated interior of the 
globe, leaving it for those who can prove their occurrence to mod- 
ify thereby the explanations here offered. Several difficulties 
ve appeared to the writer to’ strengthen the opinion advocated 
by Lyell and Poisson, that the globe, before its crust had consol- 
idated, had become so stiffly viscid as not to admit of tides, a 
condition believed to be essential to the formation of a permanent 
crust. If there were daily tides, or a westerly movement, or if 
undulations were possible, sufficient to throw up the Appalach- 
ians, why, as we have asked before, were these mighty and resist- 
less agents nearly dormant in this part of the globe till after the 
coal era? Why did they not act violently upon the Silurian 
rocks of the west, before the period that originated the Appalach- 
ians? and why not also more decidedly at the time of this great 
catastrophe? These questions are, perhaps, in part answered by 
Prof. Mather, by the argument that there would be grand parox- 
ysmal effects attending contraction, causing at long intervals, a 
violent westerly movement beneath the crust. But, again, why 
if the cause of the mountain elevations isa westerly movement 
(that is a movement from the east) beneath the erust, why should 
we have mountains on the westside of the continent. while the 
wide interior is nearly flat? And why should idnéed western 
mountains have attained such an altitude? ‘Why should the 
areas of greatest igneous action be to the west of the summit on 
the Rocky Mountains, and to the east over the Appalachian re- 
ion; that is, on the oceanic side in each ease? These are among 
the objections to the hypothesis, that internal tides or undulations 
have been a prominent agent in geological dynamies since the be- 
ginning of the Silurian epoch ; and if the explanations of phenom- 
ena, offered in this article, are at all satisfactory, they contain @ 
still weightier argument against the view. 
