ON CONGLOMERATED RpCJCS. 



r^neous formation with the limestone in which 

 they are contained, and consequently, the whole 

 mass is to be viewed as a chemical forpaa- 

 tion. 



The sandstpne-conglomerate has muph more of 

 the mechanical aspect th^n any of the rocks we have 

 at present described. Indeed, its general appear- 

 ance is so much that of a pechanical deposite, that I 

 long hesitated as tq its true nature, and it was only 

 ^fter minute and careful investigation I was induced 

 to believe, that some varieties at least of this rock 

 are of a chemical nature. This opinion, I started 

 in my sketch of the Mineralogy of the Pentlands, 

 read before the Society some time ago, and still 

 find no reason to alter it^ One of the best ex- 

 amples of the chemical sandstone-conglomerate 

 in this neighbourhood, is that at Habbie's How 

 in the Pentlands. This conglomerate, as is men- 

 tioned in my description of the Pentland Hills, is 

 com posed of variously, shaped masses of grey-wacke^ 

 grey-wacke-slate, flinty-slate, felspar, jasper, and 

 quartz, immersed in a basis copiposed of smaller 

 fragments, generally of the same minerals as the 

 larger. The most abundant of these apparent 

 fragments, are those of grey-wacke, which have 

 generally a globular or oval form, and vary in size, 

 from a walnut to that of a man's head and up- 

 wards. They aKp composed of fejspar, quarts, 

 ^nd a little mica, which are connected together 

 without any basis, or have the same mode of ag- 

 gregation as that observed in crystalline rocks, suc^ 



