ON CONGLOMERATED ROCKS. 211 



companies primitive porphyry, and with the verd 

 antique or brecciated primitive limestone. Hence 

 these rocks are to be viewed as chemical deposites, 

 and as they are the only primitive rocks exhibit- 

 ing the fragmented aspect, we are entitled to in- 

 fer, that, as far as we know at present, true con- 

 glomerates do not occur in primitive country. 



Grey-xvacke, the next conglomerated rock w^e 

 described, has been hitherto considered as a me- 

 chanical deposite. But the fragments in this, as 

 in the rocks already described, are to be observed 

 gradually passing into the surrounding mass, and 

 intermixed with it at their line of junction, and 

 apparent fragments of grey-wacke-slate, several 

 feet in length and breadth, and not more than 

 one-twelfth of an inch in thickness, which must 

 have been broken into pieces, had they been true 

 fragments, are imbedded in the grey-wacke. Fur- 

 ther, the constituent parts of the rock are fre- 

 quently connected together without any basis, in 

 the same manner as the felspar, quartz, and mica 

 in granite ; and we also observe the ingredients 

 concentrating in the basis into roundish and other 

 shaped distinct concretions. These facts go to 

 support the opinion, that grey-wacke is a chemical 

 not a mechanical deposite. 



In the conglomerated transition limestone, which 

 has excited so much attention amongst minera- 

 logists, the fragments have the same characters as 

 those in grey-wacke, conglomerated gneiss, 8cc., 

 and are therefore to be considered of cotempo- 



