Effects of Heat modified ly Compression. 20J 



svhole mass of secondary strata, in great tracts of country, 

 has been removed from above the primary, the weight of 

 that mass alone must have been sufficient to fulfil all the 

 conditions of the Huttonian theory, without having recourse 

 to the pressure of the sea. But when the two pressures were 

 combined, how great must have been their united strength 1 

 We are authorised 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 extend- 

 ing 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 Hut- 

 tonian theory, and enables us, upon its principles, to account 

 for the igneous- formation of all rocks from loose marine 

 deposites. 



The sand would thus be changed to sandstone, the shells 

 to limestone, and the animal and vegetable substances to coal. 

 Other beds, consisting of a mixture of various substances, 

 would be still more affected by the same heat. Such as con- 

 tained iron, carbonate of lime, and alkali, together with a 

 mixture of various earths, would enter into thin fusion, and, 

 penetrating through every crevice that occurred, would, in 

 some cases, reach what was then the surface of the earth, 

 and constitute lava : in other cases it would congeal in the 

 internal rents, and constitute porphyry, basalt, greenstone, 

 or any other of that numerous class of substances which we 

 comprehend under the name of wlunslone. At the same 

 lime, beds of similar 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. 

 Id this state, the particles, though far from possessing the 

 ftame freedom as in a liquid, arc susceptible of crystalline: 



arrangement ; 



