DETERMINATION OF SUCCESSIVE STRATA. 201 



not annihilated : they were embalmed, as it were, 

 where they died; and we can now dig out from the 

 bowels of the rock, an impression, or the frame itself, 

 of a fish, as clear and distinct as when it first died; 

 or a plant, with every little feathery leaf preserved, 

 as j*erfect as when it waved on that unknown land, or 

 floa'ed in that ancient sea, long centuries before man 

 drew the breath of life. 



These are the records which enable us to read the 

 early history of our globe; these mute witnesses, each 

 in its own peculiar rock, identify that rock, in what- 

 ever part of the world it may occur. There is a 

 gradual progression in their appearance. The lowest 

 fossiliferous rocks contain but few remains, and those 

 of species entirely dissimilar to any which now exist. 

 As we come down from this most remote antiquity, 

 the fossils increase in number, and also in their like- 

 ness to the forms of living species; until at last, in 

 the very latest formations, we find both animals and 

 plants nearly or quite identical with some of our ex- 

 isting kinds. A skilful geologist can always tell, 

 from its fossils, at what position in the series any rock 

 belongs. 



The number of stratified rocks is very great, but it 

 is not my present purpose even to name them: I shall 

 only show, how a knowledge of their composition 

 bears upon the practical cultivation of the soil. 



SECTION II. OF THE DIFFERENCES IN COMPOSITION AMONG 

 THE VARIOUS ROCKS. 



All of our rocks, both stratified and unstratified, 

 difTer in composition most materially. We may take 

 first, two examples of the primary, or unstratified 

 class, granite, and basalt, or trap. 



Granite is a mixture of three minerals, called quartz, 

 feldspar, and mica. The quartz is nothing but silica; 

 m the feldspar and mica, there is also silica with 



