358 Scientific Proceedings, Royal Dublin Society. 



Limestone, and on the south the Lower Limestone. See section, 

 Figure 1 (on page opposite). 



General Character of the Rocks. — In this district there is not 

 always to be drawn a hard and fast line between the different 

 varieties of the few metamorphic rocks which occur in it. These 

 consist indeed of but four classes, viz. : granitoid gneiss, gneiss 

 proper, mica schist, and quartzite. But in few cases is it possible 

 to determine a boundary between any two of them. Thus the 

 first may be seen to pass into the second, and so on. 



A good example of this is to be seen in the section west of 

 Slieve Deane, where in the space of some 400 yards, there are 

 numerous transitions of gneiss, schist, and quartzite into each 

 other, without any apparent rule or order in the process, all 

 apparently changing indifferently one into the other. 



On the whole the gneiss largely predominates, the quartzites 

 come next, and the mica schist last of all. 



Of these the gneiss is the most interesting, from a mineralogical 

 point of view ; containing, as it does, a great variety of large 

 crystals of quartz, biotite, muscovite, tourmaline, felspar (both 

 red and white orthoclase), hornblende, and olivine, and very often 

 garnets, but in minute crystals. 



It is also remarkable for a curious band of conglomerate which 

 occurs north and south of Ballydawley Lake, near Union Wood. 

 This rock is a coarse granitoid gneiss, containing lenticular blocks 

 and rounded pebbles of diorite or hornblendic rock weathering 

 out on the surface. 



South of the lake, and nearly a mile from the first exposure, the 

 same conglomerate appears, although shifted to the east by a fault. 

 Here some of the boulders are 2 feet long, and 8 to 10 inches 

 wide. The whole visible thickness of this bed, or series of beds 

 is about 200 feet, and it is an important find in one way, namely, 

 that whether we consider the diorite pebbles to be altered or not 

 from the parent rock, their presence in the gneissose beds proves the 

 existence of an older rock prior to even the formation of those beds. 



Serpentines. — Three well-marked bands of serpentine occur in 

 these rocks. The chief one appears at Slishwood, and occupies 

 the valley running nearly south from Bunowen Bay, Lough Gill, 

 for nearly two miles, and has an average width of about 500 

 feet. It will be fully described further on. Its chief peculiarity 

 is that it is highly magnetic. 



