PRIMARY. 



78 . SCIENTIFIC AGRICULTURE. 



f Clay slate, 



Quartz rock, 



Hornblende slate, 



Talcose slate, 

 j Primary limestone, 



Serpentine, 



Mica slate, 



Gneiss. 



Alluvium. If we commence at the surface of a soil which 

 has been formed by the successive deposits of annual floods, or 

 the freshets of rivers, and descend to the lowest class of rocks, 

 vi Zj the primary, we shall pass through the different classes 

 of rocks in the following order. The first few feet, usually 

 less than one hundred, is composed of vegetable and earthy 

 matters, loam, sand and fine gravel, deposited in horizontal 

 beds. 



Drift. The second formation is made up of coarse and fine 

 sand, gravel, and. sometimes clay, containing rounded masses 

 of rock called boulders. This mixture is often horizontally 

 stratified. 



Tertiary. The third series is composed of clay, sand, gravel 

 and marl, with occasional beds of quartzose and calcareous 

 rock, which have been deposited from water in a quiet state. 

 This series also contains many organic remains : the strata are 

 usually horizontal, but sometimes they have a small dip. 



Secondary. The next series below the tertiary is composed 

 mostly of solid rocks : these rocks are made up mainly of sand, 

 clay and pebbles cemented together : these are interstratified 

 by organic remains and several varieties of limestone, they 

 usually dip at various angles. The older fossiliferous rocks 

 included in this series are sometimes called transition rocks. 



Primary Transition. This class includes both stratified 

 and unstratified crystaline rocks, which are destitute of organic 

 remains. The unstratified rocks lie below the stratified ones 

 wherever they have been found : hence it is inferred that the 

 interior of the globe consists of unstratified crystaline rocks. 



