458 Analyses of Books. [Dec. 



integrant particles, having all of them the same shape, and united 

 in the same way. It is obvious that fragments of quartz, &,c. 

 can never form a crystal, because they cannot possess the same 

 shape, and they must of necessity be destitute of polarity. 



2. Partial Deposition. — Our author supposes that all the 

 materials that constitute the strata which cover the surface of 

 the earth were in solution in a fluid, and that this fluid deposited 

 more of the matter held in solution over one place than over 

 another. This would occasion inequalities in the new surface 

 formed. He ascribes these partial depositions to the action of 

 tides and currents. 



3. Subsidence. — After the strata were deposited, they often 

 gave way, and sunk either by shrinking, or by the pressure of the 

 strata deposited over them. The inequality of this subsidence 

 would occasion heights and hollows on the surface of the earth. 

 Every case of subsidence implies & fault ; but faults may exist 

 without subsidence ; for if new matter were deposited at present 

 on the surface, it is obvious that the strata could not be on a 

 level owing to the inequalities existing before this deposition. 



4. Volcanoes and Earthquakes. — The effects of these our 

 author thinks would be the same as at present. They would 

 form occasional hills by the accumulation of ashes or scoria, or 

 valleys, by the falling in of unsupported craters. 



But the action of running water, he thinks, has been in all 

 ages the principal cause of inequality of surface. 



IV. Of Formations. 



By formation is meant a series of rocks supposed to have been 

 formed in the same manner and at the same period. The term 

 was introduced by Werner, and is purely theoretical. When 

 two substances are intermixed with each other, or when they 

 alternate with each other, they are supposed to have a common 

 antiquity and origin. But our author is of opinion that neither 

 of these circumstances affords a proof of a common origin. I do 

 not see, however, how two different substances could be found 

 intermixed together, unless they had been deposited at the same 

 time. Thus granite is a mixture of felspar, quartz, and mica. 

 How is it possible to avoid concluding that these three ingre- 

 dients were deposited at the same time? In the valley of the 

 Pentlands, near Edinburgh, we find a vast number of thin beds 

 of grey wacke and greywacke slate alternating with each other. 

 How is it possible to avoid believing that these beds were depo- 

 sited nearly at the same time ? These beds stand nearly perpen- 

 dicular, and they are covered by beds of greenstone, compact 

 felspar, &c. lying nearly horizontal. How can we avoid conclud- 

 ing that these horizontal beds were deposited at a different time 

 from the perpendicular beds on which they lie? 



Werner and his followers are of opinion that formations are 

 universal, or that they extend (though with interruptions) round 



