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tions that have been made by others on their structure 

 and general character, I am disposed to consider them 

 among those the least liable to decomposition or disin- 

 tegration. 



The principal constituent part of the green- stone 

 rock is hornblende. This substance often differs in 

 its texture as well as in colour : but in general it may 

 be considered impervious to water. The other con- 

 stituent part is commonly felspar. This substance, 

 as I have before mentioned, is, in some cases when 

 combined with hornblende, subject to disintegration, 

 which gives to the rocks the appearance of a slow, 

 but progressive decomposition ; and that by reason of 

 the spicula of hornblende projecting a little beyond the 

 surface of the rock, thereby causing a harsh and 

 rough surface. 



It not unfrequently happens, in digging through the 

 earth upon a ridge of this rock, that we come upon a 

 superincumbent mass, or stratum of a pulverulent, or 

 apparently decomposed matter, having hornblende for 

 its base ; and similar to that mentioned of gneiss and 

 some other stratified rocks : but where this rock is 

 presented to view perfectly formed there is but little 

 reason to believe that it has suffered any material di- 

 minution, or loss of substance from the period at 

 which it was first formed to the present time : and 

 this opinion is founded on the following circumstances. 



Hornblende, being impervious to water, cannot be 

 liable to decomposition from any possible change of 

 temperature, that of ignition excepted. In proof of 



