152 The Irish Naturalist. 



remained fluid after the crust had solidified. In the country 

 to the south of the railway are several considerable intrusive 

 masses of hornblendic rocks, which may for the most part be 

 referred to the diorite series. This rock, in process of 

 weathering, splits readily into large blocks, and appears for 

 this reason to have been particular!}^ adapted for transportation 

 by glacial agenc3^ It is frequently met with in the form of 

 boulders in the cuttings, and erratic blocks of the same rock 

 are distributed over a wide area, being particular!}^ numerous 

 on the high ground west of the lower end of lyough Corrib. 

 Cutting all the other rocks and quite unaifected by earth- 

 movements are dykes of fresh-looking basalt and dolerite. 

 These are probably much newer than the other rocks of the 

 countr}^, and may be contemporaneous wdth the Eocene 

 basalts of Ulster. The above general account of the rocks of 

 the district will be useful for a correct appreciation of the 

 following detailed descriptions. The terms right and left are 

 supposed to apply to an observer proceeding from Galway 

 towards Clifden. 



Cutting at Oughterard. 



. This cutting is about 700 yards long, with an average depth 



of 25 feet of rock ; the diagram, fig. i, shows the right face of 



the cutting. At the Oughterard end is a dark Carboniferous 



Fig. t. 

 Signal Post. 





Yi. it. '. . i 





d Carhoniferous Limestone, q Qnartzite. q^ Fine Quartzile. 

 G Granite. A Hornblende Schist. 



limestone, with numerous minute shining specks and large 

 concretionary masses of calcite. This limestone is fossil- 

 iferous, some brachiopod shells and crinoid vStems being seen 

 in it. The undisturbed and well-bedded appearance of this 

 exposure forms a marked contrast to the crushed condition of 

 the older rocks which make up the rest of the cutting. After 

 the limestone comes a space occupied b}- the debris of the 

 neighbouring rocks, mixed with clayey matter. Next in 

 order is a great mass of crushed green quartzites, wdiich show 



