A HISTORY OF SCIENCE 



to be admitted that not merely volcanoes, but many 

 "trap" formations not taking the form of craters, had 

 been made by the obtrusion of molten rock through 

 fissures in overlying strata. Such, for example, to cite 

 familiar illustrations, are Mount Holyoke, in Massa- 

 chusetts, and the well-known formation of the Pali- 

 sades along the Hudson. 



But to admit the "Plutonic" origin of such wide- 

 spread formations was practically to abandon the Nep- 

 tunian hypothesis. So gradually the Huttonian expla- 

 nation of the origin of granites and other "igneous" 

 rocks, whether massed or in veins, came to be accepted. 

 Most geologists then came to think of the earth as a 

 molten mass, on which the crust rests as a mere film. 

 Some, indeed, with Lyell, preferred to believe that the 

 molten areas exist only as lakes in a solid crust, heated 

 to melting, perhaps, by electrical or chemical action, as 

 Davy suggested. More recently a popular theory at- 

 tempts to reconcile geological facts with the claim of 

 the physicists, that the earth's entire mass is at least as 

 rigid as steel, by supposing that a molten film rests be- 

 tween the observed solid crust and the alleged solid 

 nucleus. But be that as it may, the theory that sub- 

 terranean heat has been instrumental in determining 

 the condition of "primary" rocks, and in producing 

 many other phenomena of the earth's crust, has never 

 been in dispute since the long controversy between 

 the Neptunists and the Plutonists led to its establish- 

 ment. 



LYELL AND UNIFORMITARIANISM 



If molten matter exists beneath the crust of the 

 earth, it must contract in cooling, and in so doing it 



140 



