SiGERSON — On the Physical Geography of Ireland. 17 



In the west, whilst local tradition relates that off the west coast of 

 Achill there is a beantifiil land sunk beneath the waves, with its fields 

 and city, the physical appearance of Sliav Crnachan is^ such as to 

 suggest partial subsidence. " There are evident indications here of 

 Sliav Cruachan having been sliced down," writes the Eev. Ctesar 

 Otway,* " and left as it were the palpable remnant of some great con- 

 vulsion ; for just behind the precipice where it is highest, and about 

 twenty feet from the brow, an anterior chasm is seen, forming an 

 enormous and rugged fissure for hundi'eds of yards along — in some 

 places hundi'eds of feet deep ; and this shows that when the mighty 

 blow was given, and while half the mountain was falling down, this 

 crack took place. It was but a chance that this great slice did not go 

 down along with the rest." 



That subterranean waters exist, which, under the influence of 

 earthquake action, may be brought to light is a proven fact. In the 

 neighbourhood of Cong, the ciuious tourist may even now, by descend- 

 ing into a deep cavern, behold a subterranean river — one of several 

 streams, which, percolating through the limestone strata, convey the 

 waters of Lough Mask to mingle with those of Lough Corrib. In 

 ISlimmo's reportuponthe geological structure of Connemara, he, writing 

 of this district, says : "The fletz limestone, passing under Lough Corrib, 

 occupies the greater part of the provinces of Connaught and Leinster.'' 

 The boundary of this rock runs nearly in a straight line to Oughte- 

 rard, from Oughterarcl it turns to the north, and, crossing the lake, 

 appears on the opposite, a little to the west of Cong, and occupies the 

 southern margin of Lough Mask. The boundary now is lost in Lough 

 Mask, but reappearing at the upper or northern extremity, turns off 

 towards Westport ; about three miles short of that town, however, it 

 turns north-east to Castlebar. " It is particularly worthy of remark," 

 lie adds, " that along the borders of the fletz limestone there are series 

 of vast caverns usually with subterranean rivers traversing them. 

 Though this be a common occurrence in the limestone countries, there 

 are few instances, I believe, so remarkable as in this tract. A suc- 

 cession of lakes having no visible outlet occurs in the same situation; 

 of these, Lough Mask is by far the most considerable. The di'ainage of 

 a country of two-hundred and fifty square miles sinks here in a basin 

 of forty square miles, and after a subterranean course of two miles rises 

 in several magnificent fountains to join Lough Corrib. On the south 

 of Lough Corrib also, the Eoss Lake has no visible outlet, though it 

 receives the waters of a large tract of mountain. The waters of Lough 

 Mask are visible on the passage in several large caverns near Cong, but 

 those of E.OSS probably rise in Lough Corrib, by an inverted syphon. 

 There are two or three other smaller lakes, to the east of Eoss, and 

 probably of a similar description," 



From their geological situation, Loughs Corrib, Mask, and Conn 



* Tour in Connanglit. 

 It. I A. r-Roc. — VOL. 11., SF.i;. ii., sriExuE. 



