On the Internal Fluidity of the Earth, 511 



precession and nutation cannot furnish us with any data whatsoever 

 relative to the greater or less thickness of the solid external crust of 

 the globe. 



[In directing the attention of our readers to this most important 

 communication, which so thoroughly explains away the objections 

 lately brought forward by mathematicians and astronomers, against 

 the so-long accepted theory of the internal fluidity of the earth, we 

 would express our entire concurrence in the remarks made by M. 

 D'Archiac in the discussion of this paper, in which he expressed his 

 lively satisfaction at seeing the subject thus ably investigated by an 

 authority so doubly eminent both as an astronomer and mathema- 

 tician as M. Delaunay. Further observations upon this interesting 

 question will be found in a recent paper by Mr. David Forbes in the 

 Chemical News of October 14, vol. xviii. p. 191, to which we also 

 would refer. — Ed. Geol. Mag.] 



n. — On the Formation of Mountain Chains. 



By N. S. Shaler, Esq.i 



NOTHING shows more clearly the imperfect nature of our know- 

 ledge of the forces which have brought about the existing 

 condition of the earth's surface than the doubt which still exists as 

 to the cause of mountain chains. There have been many views 

 brought forward, some of which seemed to satisfy most of the facts, 

 but none have been sufficiently broad to include all the phenomena, 

 and the most clearly-defined result of the action of physical forces 

 of the earth's crust still remains involved in obscurity. The main 

 difficulty in the way of gaining an insight into the cause of all the 

 dynamical phenomena of the earth's surface, is the doubt which has 

 all along existed as to the physical condition of the mass of the 

 earth. Until it is decided whether the sphere is rigid to the centre, 

 or essentially fluid, with a crust floating upon its surface, it will 

 scarcely be possible to attain to anything like certainty in our 

 explanations of all the movements in the crust. Although in 

 deference to the weight of opposing opinion, we must regard the 

 question of fluidity or rigidity of the interior as still unsettled, 

 there can remain little doubt in the minds of those geologists whose 

 views are in no way influenced by the defence of long held opinions, 

 that the earth is essentially rigid, and that the condition of mobility 

 of the elements of the mass which perfect fusion gives, can not be 

 the prevailing condition of the interior. The calculations of Hop- 

 kins^ and Thomsons seem to make scarcely any other view pos- 

 sible, and the few investigations which have been made into the 

 contraction of the igneous rocks, in cooling, make it impossible to 

 conceive how a solid crust formed on a fluid interior could be 

 sustained, subjected as it has been to innumerable shocks, sufficient 

 to rupture it, and sink the fragments in the fluid below. Against 



1 From the Proceedings of the Boston Society of Natural History, June 6, 1866. 



2 Hopkins (Wm.) Phil. Trans, of the Eoyal Soc, 1836, p. 382. 



» Thomson (W.) on the Eigidity of the Earth. Proceedings of the Royal Soc, 

 Vol. xii. p. 103. 



