Shaler.] 8 [June 6, 



June 6, 1866. 



The President in the chair. Twenty-nine members present. 



Mr. T. T. Bouve gave some accomit of the minerals pre- 

 sented by Dr. C. T. Jackson this evening. The collection 

 was a large and valuable one ; many of them having been 

 obtained in former years in localities now exhausted. 



Mr. F. B. Sanborn read a letter from Mr. William B. 

 Fletcher, presenting specimens and giving an account of the 

 habits of a Darter, Pmcilichthys ccerulea of Storer, taken at 

 Indianapolis, Indiana. - , 



The following paper was presented : 



On the Formation of Mountain Chains. By N. S. Shaler. 



Nothing shows more clearly the imperfect nature of our knowledge 

 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 Hopkins* and Thompsonf seem to make scarcely any 

 other view possible, and the few investigations which have been made 



* Hopkins (Wm.) Thil. Trans, of the Royal Soc, 1836, p. 382. 

 t Thompson (W.) on the Kigidity of the Earth. Proceedings of the Eoyal Soc, 

 Vol. XII. p. 103. 



