234 ANNUAL OF SCIENTIFIC DISCOVEUr. 



the land surfaces, has effectually removed all direct proof, al- 

 though the indirect evidence is very much in favor of tiieir occur- 

 rence. From calculations based upon tin? amount of sediment 

 brou;::ht down by the Ganges, Mississippi, and other rivers, it 

 would follow that from the close of the miocene and eocene gla- 

 cial periods to the present diiy, supposing the rate of deposition 

 to be constant, 120 feet and 410 feet respectively have been re- 

 moved and carried down to the sea in the form of sediment. The 

 cosmical theory of climate also requires that if glacial conditions 

 obtained at these periods, warm and equalde climates must have 

 prevailed immediately before and after them; and the author 

 maintains this is just what has happened. In the Turin miocene, 

 congh)merates, considered glacial by Sir Charles Lycll, are over- 

 lain and underlain conformably by strata indicating a subtropical 

 condition of climate. The same phenomena are also observed in 

 Switzerland in rocks of the middle eocene period, where we iind 

 ''tiysch" closely associated with nummulitic strata, which c(mtain 

 genera characteristic of a warm climate. The cretaceous and 

 permian periods aflbrd similar evidence, and in the post-pliocene 

 glacial period we have undoubted evidence of a warmer climate 

 during part of its duration, as evidenced by the occurn^nce of ani- 

 mals and shells existing in latitudes where they could not other- 

 wise have lived in consequence of the cold. — Chronicles of Sci- 

 encCf Jan., 1869. 



THE SOURCE OP VOLCANIC ACTION. 



The limitation of volcanic activity to the seashores was long 

 since noticed, and has been much commented upon. A careful 

 study of the relation of former seats of igneous activity to the an- 

 cient seashores will convince the student that volcanoes always 

 cease to be active when the ocean abandons their bases. It is 

 evitlent, therefore, that we must seek the origin of volcanic action 

 in some processor other whicii is going on in the crust of the earth 

 beneath the sea floor, which does not take place beneath the dry 

 land. 



There is but one cause competent to produce such effects which 

 is peculiar to the sea, and that is the accumulation of strata going 

 on upon its floor. The beds flrst laid down contained, it may be, 

 large quantities of organic matter in the shape of animal and plant 

 remains, and a great deal of wattn' was imprisoned in their struc- 

 ture. After a time the accumulation of superincumbent beds 

 causes the heat of the beds flrst laid down to become very great. 

 A thickness of sedimentary beds much less than what we have 

 good reason to supj^ose may have been laid down on the greater 

 part of the ocean floors, would be suflicient to In'ing tiie heat of ma- 

 terials lying at the level -of the original sea Ijottom to a temperature 

 high enough to decompose the water and vaporize the carbon 

 which they contained. As this heat increased, the tension of these 

 materials seeking to take on the gaseous form would become 

 greater and greater. If at any point the pressure was suddenly 



