306 ACTION OF HEAT MOE^IFIED 



Tbeorv'; without having recourse to the pressure of the sea. Bui 



when the two pressures were combined, how great must have 



been their umted strength I 



We are authorized to suppose, that the materials of our strata, 



in this situation, underwent the action of fire. For volcanoes 



have burnt long before the earliest times recorded in history, as 



appears by the magnitude of some volcanic mountains ; and it 



can scarcely be doubted, that their fire has acted without any 



material cessation ever since the surface of our globe acquired 



its present form. In extending that same influence to periods 



of still higher antiquity, when our strata lay at the bottom of the 



sea, we do no more than ascribe permanence to the existing laws 



of nature. 



The combination of heat and compression resulting from 



these circumstances, carries us to the full extent of the Hutto- 



nian Theory, and enables us, upon its.principles, to account for 



the igneous formation of all rocks from loose marine depc- 



sites. 



Enumeration The sand would thus be changed to sandstone ; the shells to 



oftiie effects of |jj^^gj.yj^g ^^^ ^^^ animal and vegetable substances to coal. 



heat under this ' ^ 



pressure in pro- Other beds, consisting of a mixture of various substances^ 



due ng the van- ^^^^^1 J be still more affected by the same heat. Such as con- 



ous stony mat- -^ 



ters now found, tained iron^ carbonate of Ume, and alkali, together with a mix- 

 ture of various earths, would enter into thin fusion, and, pe- 

 netrating Liirough every crevice that occurred, would,in some 

 cases, redch what was then the surface of the earth, and con- 

 stitute lava: in other cases, it would congeal in tlie internal 

 rents, and constitute prophyry, basalt, greenstone, or any other 

 of that numerous class of substances, which we comprehend 

 under the name of •uyliinsfoiie. At the same time, beds of simi- 

 lar quality, but of composition somewhat less fusible, would 

 enter into a state of viscidity, such as many bodies pass through 

 in their progress towards fusion. In this state, the particles,, 

 though far from possessing the same freedom as in a liquid, are 

 susceptible of crystalline arrangement ;* and the substance, 



which,. 



* This state of vjscidity, with its numberless modifications, is de- 

 serving of great atlention^ since it aflbrds a solufcion of same oi the 

 most important geological questions. The mechanical power ex- 

 erted b}' some substances, in t!ie act of assuming a crystalline form, 



