490 Report of the State Geologist. 



As regards these finer gneisses, there is a series of facts analogous to 

 those described in the coarser rocks, so far as the inclusions are concerned. 

 At many widely separated points, the fine pink and grey gneisses have been 

 found to contain masses of very dark, rather fine rock. As it seemed probable 

 that these masses might have some bearing on the problem in hand they were 

 examined w ith care, and in many cases were sketched, or photographed. They 

 may, for convenience of discussion, be divided into two groups: long narrow 

 bands, and irregular masses. 



The bands vary in width from a few inches up to two feet or more, and 

 may be some rods in length. They are seldom, however, continuous for any 

 such distance, being divided into segments, evidently at .one time continuous 

 but now separated by masses of gneiss, from a fraction of an inch to several 

 feet in width. To form these segments the bands have been broken squarely 

 across, so that the blocks have a nearly rectangular or a rhomboidal outline. 

 The dark rock of the bands is usually imperfectly gneissoid, with foliation 

 parallel to the sides of the bands. Sometimes little fractures or gashes extend 

 into the bands from either margin, and are tilled with the material of the 

 surrounding gneiss. Often several of these bands occur close together, when 

 they are usually parallel with each other, as they nearly always are with the 

 foliation of the gneiss. The filling of narrow cracks and veinlets in the bands 

 is often coarser than the surrounding gneiss, but as these become broader, 

 and adjacent blocks are more widely removed from each other the filling 

 material becomes identical w ith the normal gneiss. 



Several explanations may be suggested for the presence of these bands, 

 and these may be briefly considered. In the first place, they may be regarded 

 as indications of bedding in the gneissic series, in which sense they were 

 alluded to above. But their limited and irregular occurrence, as well as their 

 slight extent and sudden termination along the strike oppose this view. 

 Other objections will appeal- in speaking of the next supposition. According 

 to the latter, the bands are dikes intruded in parallel groups, and broken up 

 by subsequent pressure. At first sight this is a very plausible view, but it 

 seems to be completely negatived by the peculiar separation of the bands into 

 distinct blocks. Such blocks might result from faulting, but, in this case, no 

 faulting has occurred ; w hile, if the dikes had been separated by stretching, 

 the resultant blocks would have a tapering, elliptical shape, totally different 

 from that they show. It is impossible to believe that under pressure the 

 dikes would break into blocks, which would retain a rectangular outline, 

 while the surrounding solid gneiss, under the same pressure, flowed around 



