500 Scientific Proceedings, Royal Dublin Society. 



that the water here could never have escaped at a lower level than 

 that of its present retaining rock-bar, so as to permit of the sunken 

 forest trees having flourished in the air, without the supposition of 

 earth movements having taken place since the peat and trees occu- 

 pied the subaerial surface, movements which had considerably- 

 altered the position of the ground to be drained with regard to 

 previously existing levels. 



Further seaward, along Sligo Bay, there are indications, in 

 raised beaches, that an upward movement of the land took place ; 

 and I found, many years ago, shells of the common sea mussel in 

 a sand-pit, not far from the old coach-road between Sligo and 

 Ballysodare, upon part of the high drift-covered ground lying 

 between Lough Gill and Ballysodare Bay. In these cases the 

 indication is of an elevation in recent times, which might here or 

 there pond back the terrestrial water, but which must have had 

 regions of singularly local intensity, if it can be at all supposed to 

 have caused limited land spaces to become permanently submerged, 

 as in the case near Ardachowen, on the Sligo river. 



Turning now to Lough Arrow, near Boyle, we find this to be 

 a large lake, with irregular outline, four and a-half miles in length, 

 by a mile to two and a-half miles in breadth, bordered by hog- 

 backed hills of drift near its margin, similar hills forming islands 

 within it, while it is surrounded by nearer, or more remote, moun- 

 tainous elevations, such as the Greevah Hills, formed of coal-measures, 

 on one side, or the carboniferous limestone elevations of Knockna- 

 horna and Kesh, on the other, or the termination of the pre-carbon- 

 iferous Curlew Mountains towards the upper, or Boyle end of the lake. 

 The lake itself is peculiar in having no rivers to supply it beyond 

 the little brook from the Curlews, which empties itself into it at 

 Ballinafad. The lake water is clear, and is probably largely sup- 

 plied by springs, seeing that a considerable stream issues from the 

 lake, passing over a rock barrier near where it starts, at Annagh 

 or Ballyrush, and eventually reaching the sea at Ballysodare. 

 Another peculiarity is that this large lake is at one point sepa- 

 rated by a distance of only a few hundred yards from Lough Kej", 

 one of the lakes of the basin of the Shannon, with which that of 

 Lough Arrow has no connexion. 



The shores of Lough Arrow, where not formed of drift, are in 

 various places composed of peat, locally known as " The Black 



