PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 741 



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once in a state of liquefaction by heat, appears to corroborate such 

 ideas. It must not be forgotten that all our observations have 

 been made near the surface, and that we have explored but a small 

 portion of the exterior of our planet, say ten miles; while accord- 

 ing to late calculations the crust of the earth is eio'ht hundred 

 miles thick. The crust is occupied by distinct mineral masses or 

 rocks which are divided into four great classes: Aqueous or sedi- 

 mentary, or fossiliferous; Volcanic, or unstratified, and in which 

 no fossils are found; Plutonic, which form the lofty mountains, 

 and MetcnnorpJiic, or stratified crystalline rocks, which are the 

 slates or schists, such as gneiss, mica schist, clay slate, chlorite 

 slate, etc., and correspond in form and arrangement to those of 

 sedimentary formation, and which, according to the Huttonian 

 theory, were originally deposited from waters, but were after- 

 wards so altered by subterraneous heat as to assume a new 

 texture. 



It was supposed that granite was first formed together with a 

 crystalline or metamorphic strata, and therefore called primitive, 

 and that the Neptunian or volcanic rocks were afterwards super- 

 imposed, but that all formations, whether stratified or unstratified, 

 earthy or crystalline, with or without fossils, were alike regarded 

 as of aqueous origin. In the middle of the last century Lehman 

 divided the rocks into three classes: the first and oldest he called 

 primitive, which comprised the plutonic and metamorphic rocks; 

 the next he called secondary, including the aqueous or fossiliferous 

 strata; and the third, alluvial, formed at the deluge. The origin 

 of the first was purely chemical; granite and gneiss, with no organic 

 remains, therefore antecedent to the creation of living beings, and 

 coeval with the birth of the world itself The secondary forma- 

 tions must have been mechanical deposits, produced after tlie 

 planet had become the habitation of plants and animals. This 

 theory was lately improved by Werner adding a transformation 

 between the primitive and secondary. The Neptunian theory of 

 Werner became a great favorite; he went so far as to class trap- 

 pean rocks — the origin of which was fully demonstrated to be 

 igneous — in the aqueous, and as mere subordinate members of the 

 secondary formations. That volcanic action must have been a very 

 powerful agent when in connection with water leaves no doubt, 

 and it must be considered that in a large portion of the earth live 

 volcanoes have existed for ages, and are still in existence. From 

 a consideration of a magnificent eruption of a volcano seen by him 



