154 LABORATORY LESSONS IN GENERAL SCIENCE 



ORIGIN AND NATURE OF SOILS 



1. Examine specimens of quartz, feldspar, hornblende, and 

 mica. Describe each with respect to its characteristic appear- 

 ance. Be sure to take note of any differences in appearance 

 of specimens of the same kind of mineral (usually due to ad- 

 mixture of other earthy material). It is to be remembered 

 that each of these substances in a pure state is a somewhat 

 complex chemical compound of definite composition. After 

 becoming familiar with these type specimens so that they 

 are readily recognized at sight, identify any specimens that 

 may be assigned you by numbers only. 



2. Examine specimens of several different kinds of granite, 

 and be able to point out in them particles of quartz and 

 feldspar, as well as any hornblende and mica (if present). 



Examine specimens of "weathered granite." State which 

 of the constituent minerals seems to possess greatest re- 

 sistance to decomposition. 



Whether at the seashore or inland, and however exten- 

 sive its amount, sand may be considered as quartz particles 

 derived from granitic rock. Clay is feldspar decomposed. 

 Explain how it is that clay and sand, possibly from the same 

 rock sources, are frequently found as deposits entirely dis- 

 tinct, and often widely separated. Account for sandstone 

 as a rock. Explain why it is that sandstone so often exhibits 

 a stratified form (an arrangement in layers). 



3. Rub some dry clay between the thumb and finger. 

 With a magnifying glass note in a general way the size of the 

 clay particles as seen when scattered over the surface of white 

 paper, 



