THE GNEKSSOID GKxVNITES. 169 



From tlieir compositifni and structure it is evident that tlie acid scliists 

 associated witli tlie greenstone-conglomerates, as well as these latter i-ocks 

 themselves, are tiiffaceous deposits which suftered d-s-namic metamor})hism 

 and weathering until their original composition was entirely changed. The 

 darker-colored schists have now the characters of "schalsteins; " the lighter- 

 colored ones are sericite-schists. The former were originally basic tuffs, 

 and the latter, in all probability, acid ones interstratified with the former. 

 The basic rocks are nuich the more abundant. The pebbles occurring in 

 the conglomerates are all of the same general character. They are A^ery 

 similar to the schistose matrix in which they are embedded, but are less 

 schistose. They nuist be looked upon as volcanic bombs or as large frag- 

 ments of the lavas whose ashes produced the matrix. If fragments, they 

 have become rounded by the mashing that caused the foliation of the finer 

 particles. 



Since the green schists are surface materials, thev must have been 

 deposited upon some previously existing basement. This basement has not 

 yet been identified. It can not be the gneissoid granite, for the granite is 

 intrusive in the schists. 



THE GNEISSOID GRANITES. 



The granites and gneisses of the Northern Complex are closely related 

 genetically. Both are coarse-grained, both vary in color from dark greenish- 

 gray to Ijright-red, both are usually gTanular, and occasionally jiorphyritic, 

 with large red phenocrysts lying in a coarse red groundmass, and both 

 have sufi'ered more or less severely the effects of mashing. The gneisses 

 differ from the granites only in the perfection of the foliation that has been 

 imparted to them and in the amount of dynamo-clastic material discover- 

 able in them. The gneisses are indisputably foliated |)hases of the granite, 

 which is always more or less schistose. Since the origin of these gneisses 

 is known, it seems better to designate them by a name that will indicate 

 their origin, leaving the term "gneiss" to cover those foliated rocks of the 

 composition of gi'anite whose origin is problematic. 



DISTRIBlfTlON AND TOPOGRAPHY. 



The gneissoid granites occupy two distinct areas in the Northern 

 Complex. Although widely separated, the rocks occurring within them 



