492 Kinalian — Formation of Rock-basins. 



tlie south end, while it gradually deepens toward the north, and on 

 the north of the line the soundings still gradually become deeper 

 until they reach a tract over 100 feet deep (g on Map, PI. XVIII.), 

 which lies about two miles south of Cong (h on Map, PL XVIII.). 

 That a little east of this pond is a deep isolated hole, 152 feet (i on 

 Map, PL XVIII.) ; also between this pond and Innis Micatreer (j on 

 Map, Plates XVIII. and XIX.) there is a long deep patch that bears 

 about N.E. and S.W. ; and S.W. of the pond there are four long 

 deeps which have similar bearings ; while, surrounding these deep 

 places, there is a tract that also has a similar general bearing, over 

 50 feet in depth. This area, over 50 feet deep, including the deep 

 patches, is called by the fishermen on the lake " The Old Lough." 



At Inchagoil (p on Map, PL XVIII.) there are limestones in situ, and 

 also at Cong ; it may therefore be safely concluded that part at least 

 of " The Old Lough " is in a limestone country, and as these lime- 

 stones are cavernous, which is proved by the subterranean passages 

 and caves between Loughs, Mask and Corrib, there may also have 

 been an underground passage from " the Old Lough." If this was 

 the case there would be from one of the lowest parts of the lake — 

 the part to where all the southern portion has a gradual fall — a 

 passage, into which the drainage of the " Eock-basin " would flow. 

 These streams, combined with the other subaerial agencies, might, 

 even though in the smallest degree, have helped in excavating that 

 basin.^ 



That large tracts of country are drained through subterranean 

 rivers is a well-known fact. In Ireland there are many such river 

 systems ; one of the largest being at Gort, county Galway, where 

 miles of country drain into Coole Lough, and from thence through 

 subterranean passages, five miles long, into the sea at Kinvarra. 

 The subterranean river from " The Old Lough " would have been 

 at the least 18 mUes long. 



The foregoing theory might account for the formation of a portion 

 of the ''Eock-basin," but there is still the bay that leads uj) to 

 Maum, where, near its entrance and due north of Cam Seefin (d on 

 Map, PL XVIII), there is another "deep" that consists of a long 

 narrow gut, over 100 feet, surrounded by a margin over 60 feet deep, 

 (e on Map, PL XVIII). This deep could scarcely be accounted for in a 

 similar manner to that just now mentioned in connection with "The 

 Old Lough ; " for while part at least of the latter may be in lime- 

 stone and excavated as suggested, the whole of this gut must have 

 been denuded out of the hard metamorphic rocks ; and as caverns 

 or subterranean passages are rare in them, there could scarcely be an 

 underground passage from this place ; and if there was not, sub- 

 aerial action would have no power to excavate it.^ Neither is it 



1 Any one who can look so far back may bring in this name — " The Old Lough '^ — 

 as evidence in favour of this theory, as the place may be so called from a tradition 

 handed down from the Pre-glacial men " of the time when the lake did not exceed 

 these limits." 



2 Full particulars about the Coole Lough water-basin are given in the Mem. Geol. 

 Survey of Ireland, Ex. sheets 115 and 116 p. 7. 



3 What might be considered in favour of a subterranean passage out of this gut is, 



