MODIFIED by COMPRESSION. 173 



prefent form. In extending that fame influence to periods of 

 ftill higher antiquity, when our ftrata lay at the bottom of the 

 fea, we do no more than afcribe permanence to the exifting 

 laws of nature. 



The combination of heat and compreffion refulting from 

 thefe circumftances, 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 loo fe marine depo- 

 fites. 



The fand would thus be changed to fandftone ; the fhells to 

 limeftone ; and the animal and vegetable fubftances to coal. 



Other beds, confuting of a mixture of various fubftances, 

 would be ftill more affected by the fame heat. Such as con- 

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

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

 netrating through every crevice that occurred, would, in fome 

 cafes, reach what was then the furface of the earth, and con- 

 ftitute lava : in other cafes, it would congeal in the internal 

 rents, and conftitute porphyry, bafalt, greenflone, or any other 

 of that numerous clafs of fubftances, which we comprehend 

 under the name of whinjlone. At the fame time, beds of fimi- 

 lar quality, but of compofition fomewhat lefs fufible, would- 

 enter into a Hate of vifcidity, fuch as many bodies pafs 

 through in their progrefs towards fufion. In this ftate, the 

 particles, though far from poflefllng the fame freedom as in a. 

 liquid, are fufceptible of cryftalline arrangement * j and the 



fubftance 



* This ftate of vifcidity, with its numberlefs modifications, is deferving of 

 great attention, fince it afFoids a folution of fome of the molt important geologi- 

 cal queftions. The mechanical power exerted by fome fubftances, in the adl of 

 offumwg a cryftalline form, is well known. I have feen a fet of large and broad 



cryftals 



