1813.] 



On Formatious, 



191 



Note by the Editor. — What is called vis viva, and trans- 

 lated in the preceding paper living force, is a mode of expression 

 much used by the philosophers on the Continent, though not 

 familiar in Britain. It means nothing more than that the square 

 of the velocity multiplied into the bodies continues unaltered 

 before and after the shock, oscillation, &c. to which the bodies 

 are subjected. 



The following explanation of the oscillating column suggested 

 by Sir Charles Blagden appears to me much more intelligible 

 than the one in the text : — 



Let A be the interrupted sj-phon. Suppose 

 both legs full of water up to a certain height, and 

 that we continue to pour water into the short leg. 

 Part of that ^vater will spend the whole of its 

 impetus in striking against the water in the long 

 leg, and then escape at the interruption of con- 

 tiguity ; so that in fact the water in the longer leg will be ex- 

 posed to a greater pressure than it otherwise would be, and must 

 of course rise higher. 



Article VII. 



On Formations. By Robert Jameson, Esq. F.R.S.E. Professor 

 of Natural History, and Keeper of the Museum in the Uni- 

 versity of Edinburgh, &c. 



On a general view of the materials and structure of the crust 

 of the earth, we are struck with the simplicity of the whole. 

 Not more than 250 species of simple minerals have hitherto been 

 discovered ; and if we abstract the metalliferous, saline, and 

 inflammable species, there remain not more than 134 species of 

 earthy minerals. Still, with this small number of species, nature 

 might have formed many hundred distinct, compound, and - 

 simple rocks ; but it is otherwise. She employs almost exclu^ 

 sively a few species in the composition of all the rocks, both 

 simple and compound, of which the crust of the earth is com- 

 posed. Felspar, quartz, mica, minerals of the hornblende 

 family, and limestone, are the most frequent and abundant : of 

 these nearly the whole crust of the earth is composed : thus 

 granite, gneiss, mica slate, clay slate, gabbro, porphyry, sienite, 

 greenstone, basalt, serpentine, sandstone, are composed of one 

 or more of the four first mentioned substances; and the various, 

 primitive, transition, and floetz limestones, that often form exten- 

 eive ranges of mountain and tracts of country, are composed of 

 carbonate of lime. Indeed, all the species of mountain rqcks, 



