Geological Notes from West Galway, 155 



Between the last cutting bj^ the lake and the bridge are 

 coarse and fine hornblende schists. On the left side a small 

 intrusion of garnet-rock may be seen in the schist. This 

 garnet-rock is of frequent occurrence in the country south of 

 the Maam Bay arm of lyOugh Corrib ; but, being a very friable 

 rock, it has suffered much from denudation and does not form 

 a prominent feature. A little farther on are veins of coarse 

 felspathic granite, which cut both the normal granite and the 

 schist. The felspar in these veins is dark grey or black, 

 resembling labradorite ; it gives a lime reaction in the blow- 

 pipe-flame, and I have also verified the presence of lime by 

 microchemical reactions. 



Some fluor-spar may be seen in the joints in the granite, 

 and there is a small vein of haematite in the schist. At the 

 same place a wide dyke of fresh-looking dolerite crosses the 

 line ; this rock weathers brown, with numerous whitish star- 

 shaped markings. 



The cutting between the bridge and the public road consists 

 at the lake end of a mass of whitish rock, which contains what 

 appear to be fragments of altered hornblende-schist, and may 

 be due to the disintegration and alteration of that rock. 

 Farther on, a wide dyke of dolerite, similar to that last 

 described, is cut through. 



Between the public road and I^oughaunierin are some very 

 micaceous quartz schists, and much crushed hornblendic 

 schist. Opposite the houses on the road-side, veins of fels- 

 pathic granite with black felspar may be seen in the schist, 

 while near the lake there is a dyke of dolerite. North of 

 Tawnagh-beg I^ake there is a considerable cutting in granite, 

 which is much crushed, and appears to occupy part of the 

 Maam Valley fault of the Survey. The joints of the granite 

 are generally much chloritised, and the rock is traversed by 

 many veins of pure quartz, which are also bounded by chloritic 

 matter. The quartz was probably deposited from hot waters, 

 at the close of the granite intrusion. Some well-formed clear 

 quartz crystals are to be seen in hollow portions of the veins. 

 The chloritic matter on the edges of the veins effervesces 

 strongly with acid, which probably indicates the presence of 

 carbonate of lime ; and in one specimen from this cutting a 

 mass of garnet with barytes is seen on the edge of the quartz 

 vein. 



