SOS 



from this cause, to disintegration, are small in number 

 and therefore extremely limited in these results. 



There are, likewise, a variety of mineral substances 

 liable, from their structure, in a greater or less degree, 

 to the absorption of water. Repeated exposure of sub- 

 stances in this state, to the heat of the sun, is another 

 cause of a slow disintegration ; but the most powerful 

 agent in the decomposition of rocks, of any perhaps to 

 which they are exposed, is the operations of cold, when 

 it arrives at the freezing point. Very few of the in- 

 compact or imperfectly formed mineral substances, 

 when having absorbed a quantity of water, and being 

 exposed to freezing, can resist the force of its opera- 

 tions, nor long preserve their form entire. 



But even the effects of this agent, as powerful as it 

 may be, are, nevertheless, limited ; and it is only on 

 such rocks as are destitute of a cement, that it can ex- 

 ercise its powers to a degree sufficient to destroy their 

 texture, and cause a disintegration. Of this we have 

 sufficient proofs in the effects which are produced on 

 all mineral substances by its operation. A rock or 

 stone having, by exposure to rains, &c. absorbed a 

 quantity of water, and in that state exposed to in- 

 tense cold, and repeatedly frozen, is gradually reduc- 

 ed to sand or dust ; and in the following manner : 

 The water absorbed by mineral substances, insinu- 

 ates itself between all, the particles to a certain depth 5 

 by freezing, it expands, and the cohesion of the par- 

 ticles is thereby destroyed and broken up. As soon 

 as the weather moderates so as to dissolve the ice, 



