ON CONGLOMERATED ROCKS. ^13 



&s granite and syenite. The basis in which these 

 apparent fragments are contained, is of the same 

 nature with the fragments themselves, and it 

 therefore is also of a crystalline nature. But it 

 may be said, that these apparent fragments are iii 

 reality true fragments imbedded in a crystallized 

 basis ; but this cannot be the case, because they 

 do not exhibit water-worn of fractured surfaces, 

 and are to be observed passing by imperceptible 

 degrees into the substance of the basis in which 

 they are immersed. A further proof of the truth 

 of the opinion now stated, is afforded by the ap- 

 pearance which the basis itself at times assumes. 

 Thus, we sometimes observe the ingredients of 

 the basis concentrating into indistinct globular 

 masses, which are harder than the general basis ; 

 and, in other instances, the concentration of the 

 parts, is still more distinct, and the globular con- 

 cretions thus formed, are so strongly marked, as 

 not to be distinguishable from the large apparent 

 fragments. 



Sandstone, another of the conglomerated rocks 

 we described, is in general supposed to be sand 

 agglutinated by means of a clayey, calcareous, or 

 quartzy basis, and hence it is said that all sand- 

 stones are mechanical deposites. This opinion, 

 I suspect, is not correct, because appearances in se- 

 veral of the sandstctoes of this country, seem to 

 intimate, that these, at least, are more of a che- 

 mical than of a mechanical nature. These sand- 

 stones, v;hen examined with the glass, appear to 



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