50 



KNOWLEDGE. 



[Febkuaky 1, 1897. 



at a lower level than the Holy Well, never runs dry. 

 However, the main body of the river does not appear to 

 travel by this path, aud is probably more deeply buried in 

 the earth. In winter a river runs the entire distance 

 between the lakes, but in summer the channel (part of 

 which was, I believe, intended to be a canal) presents very 

 peculiar features. While the water at times sinks, at 

 other times it comes in again, and instead of rising from 

 the bottom it sometimes enters at the side at above the 

 level of the stream, making a kind of little waterfall. 

 It is but a short distance above Cong that the last portion 

 of this stream disappears. The canal to which I referred 

 was abandoned on account of the difficulty of making 

 it staunch. The water would leave the channel and 



Strcum running from under the Rock, near t'astlebar. 



then burst in again, sometimes from the bottom and 

 sometimes from the sides. A specimen of this can still 

 be seen in the village of Cong, or, at least, could when 

 I was last there. There are three places near Cong — • 

 two of them in Ashford demesne — to which visitors 

 can descend to a considerable depth to see the underground 

 streams. The third, known as the Pigeonhole, is the 

 largest, and the underground cavity can be followed for a 

 considerable distance. But when the level of Lough Mask 

 is considerably raised in winter, new features present 

 themselves. Streams suddenly burst up in the dry lands 

 on the side of the hill between Cong and Douagh, and 

 after running for some time with considerable force — 

 pulling down any of the loose stone walls that come in 

 their way — they disappear again. One of the largest of 

 the streams whose disappearance I noticed in this way, 

 rushed into what was called a water-hole — a small hollow 

 where water remained throughout the year, and the cattle 

 used to drink. I suspect that the bottom of this water- 



hole communicated with Lough Mask, and that a fissure 

 at a somewhat higher level led to Lough Corrib. The 

 ground where these outbursts took place lay so high that 

 the water must have come direct from Lough Mask — or, at 

 all events, from a part of the intervening river nearly on 

 the level of the lake — and the distance travelled by the 

 underground stream was probably not less than three 

 miles. Yet the water never flowed in these channels for 

 more than two or three days at a time, and it was only of 

 a very wet winter that it flowed there at all. The peasants 

 spoke of the direction of the wind as afl'ecting it, but I 

 think this could hardly be the case. 



I shall now pass on to the other extremity of the district 

 — Aylemore, near Westport. The river at Aylemore runs 

 for about two miles underground, and then rises again and 

 continues into Lough Mask, from which it issues in the 

 manner already described. Aylemore struck me so much, 

 and seemed so little known, that I got some photographs 

 of it taken. The stream runs straight at a steep, rocky, hill 

 — a limestone hill bounding the limestone district in that 

 direction — its bed sinking as it approaches, and then it 

 dips under. Plainly, however, the fissures are not very 

 large. On the day that I visited Aylemore there had 

 been a recent flood, whose limits were marked by some 

 hay that had bee:) carried away by the current. Close to 

 the limestone ridge the hay-line could not, I think, have 

 been less than seventy feet above the bed of the stream, 

 which probably had not been raised ten feet by the flood 

 somewhat higher up. The channels in the rock had 

 evidently been too constricted to carry away the water, 

 and a little lake had formed for the time being. But it 

 had quite disappeared when I saw it, and the stream ran 

 under the rock with a fairly rapid current. 



The whole of this district must be scooped and caverned 

 to an immense extent, yet I never heard of anything like 

 the shock of an earthquake. Probably the caverns are 

 not far enough below the surface for that purpose, and 

 that if one fell in the shock would only be felt for a few 

 hundred yards, which, in a sparsely populated district, 

 might remain quite unnoticed. W. H. S. Monck. 



LUNAR RAINBOWS. 

 To tlie Editors of Knowledge. 



Sirs, — The September Number of Knowledge has lately 

 come to hand, and I have read with interest your corre- 

 spondent, Mr. Sair's letter from Bhamo. At the beginning 

 of 1890 I saw a lunar rainbow at Ponta Delgada, St. 

 Michael's, Azores. The colours could not be distinguished 

 — only a whitish band. In 1893 I saw another lunar 

 rainbow at Para, as I was looking out over the Amazon, 

 and in this the colours could be distinguished. About 

 the same time I saw a triple sun's rainbow, the colours 

 being distinct in the first two, but the third was like the 

 lunar rainbow at St. Michael's — simply a whitish band. 

 I do not know if these phenomena are common in the 

 tropics, and should be glad if you could enlighten me. 



Manaos, Kiver Amazon. Eric H. Jackson. 



[Lunar rainbows are necessarily rather rare phenomena, 

 but are probably as often witnessed here, by those who 

 look for them, as in the tropics. — E. Walter Maunder.] 



BACILLUS IN COAL. 

 To the Editors of Knowledge. 

 Sirs, — It is, perhaps, unnecessary for me to remind 

 readers of Knowledge that the application of the micro- 

 scope to geology has vastly enlarged the borders of that 

 science, and that one of its most recent results is to show 

 us the existence of the bacillus in coal. However, a French 



