262 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



and he ascribed the domal form of the trachyte mountains not 

 to the swelling up of homogeneous masses, but to successive 

 outbreaks of viscid lava streams. Neither did he draw any 

 fundamental distinction between volcanic eruptions on land 

 and those on the ocean-floor. Cones of erupted material form 

 in the case of submarine as well as continental volcanoes, 

 but owing to the distribution of the material by water, the 

 layers of volcanic rock are less highly inclined and generally 

 of tufaceous character. Some submarine volcanoes have their 

 cones of ejection built up by repeated additions until they 

 rise above the surface ; others (e.g., lie de France, Teneriffe, 

 Palma, the Coral Islands in the Pacific Ocean) may, in Scrope's 

 opinion, have been arched to their present position by the 

 subterranean forces of heat. The difference between the 

 "craters of elevation " of Von Buch and the uplifted islands 

 of Scrope is that the former are supposed to have received 

 their characteristic form and their crater, independently of any 

 accompanying phenomena of eruption, merely by the upward 

 swelling and fracture of the crust, whereas Scrope thinks the 

 elevated submarine islands of volcanic rock are in all cases 

 originally cones of erupted rock-material accumulated super- 

 ficially round an orifice, and afterwards upraised as a whole. 



Von Buch's " Serial Volcanoes " are explained similarly by 

 Scrope as volcanic cones which participated in a crust-uplift. 

 All volcanoes, according to him, occur upon crust-fissures; 

 some eruptive vents are permanently closed, and others 

 continue to remain in communication with the earth's 

 interior, and are the scene of periodic eruptions. These 

 open vents, by affording a ready passage for subterranean 

 lava, vapours, and gases, serve to protect the neighbourhood 

 from earthquakes. Scrope attached little tectonic import- 

 ance to the elevations at volcanic fissures, regarding them as 

 quite local in effect, and having no immediate connection with 

 the regional crust-movements which elevate continents and 

 mountain-systems. 



The above are the leading doctrines of volcanicity taught 

 by Scrope, and they may be said to have laid the first secure 

 foundation of present conceptions of eruptive phenomena. 

 The chief merit of Scrope's work consists in the convincing 

 demonstration it gives of the origin and composition of vol- 

 canoes, in the disproof of the Elevation-Crater theory, and in 

 the description of a superheated subterranean magma saturated 



