impervious to water. The latter when combined with 

 the former so as to form perfect compact granite, and 

 its subdivisions, is therefore impervious to water. 



Limestone, with most of its modifications, being a 

 homogeneous substance, is likewise, when compactly 

 and perfectly formed, impervious to water. Or, if it 

 be contended that either of those rocks is slightly sus- 

 ceptible of the absorption of water, the cohesive power 

 of its structure is such, that the most intense cold or 

 frost does not, nor cannot promote its disintegration. 



Having demonstrated, I think, that the disintegra- 

 tion of rocks in general, is not materially promoted by 

 any chemical process, arising from natural causes, and 

 which will apply in a particular manner to those of 

 granite and limestone, I shall proceed to inquire whe- 

 ther these tw T o species of rocks are really susceptible 

 of disintegration from any natural cause and to what 

 extent. 



In assuming this ground, I do not mean to contend 

 that granite has not, in some instances, been found evi- 

 dently impaired in its structure, and apparently in a 

 progressive state of decomposition. The beryl and 

 apatite are both found near Baltimore, in a vein of 

 loose granite, running through gneiss, and which is ea- 

 sily broken up and crumbled to pieces ; but this is in 

 consequence of its imperfectly formed structure : the 

 quartz inclined to be granular; the mica in broad 

 pieces ; the felspar in large crystals, or rhomboidal 

 masses ; the whole unconnected and without any ce- 

 ment. Through this the water has penetrated, and, in 



