Notices of Memoirs — W. W. Watts— Tarns near Snoicdon. 565 



The fundamental position has, I maintain, not been shaken, either 

 by mathematical physics or geological facts. The more the theory 

 is tested by the light of practical geology the more remarkable is the 

 explanation it affords of the associated phenomena of sedimentation 

 and mountain-building ; denudation and faulting. Furthermore, no 

 other tlteory yet brought forward attempts to offer an explanation of 

 more than one set of these phenomena, namely, those of compression. 

 Normal faulting cannot be accounted for by compression, yet the 

 riA^al theory of tangential pressure on the crust through the shrinkage 

 of the earth's nucleus provides for compression only. Contraction, 

 by which I have shown that normal faults are produced, is not part 

 of the machinery of any other theory than the one associated with 

 my name. 



I ask geologists to bring to the consideration of these great 

 problems clearness of vision, for, usually, a single aspect only is 

 examined, the rest being left in an impenetrable haze. 



I trust I have now brought sufficient evidence before you to show- 

 that a broad examination of the formations of these islands, and their 

 associated physical phenomena, throws a good deal of light on the 

 problems of mountain-building, and that their remarkable relations 

 are well worth more detailed examination than I have been able 

 to give them in this address. 



I^rOTIOES OIF IvTIBIMIOIE-S. 



I. — Notes on some Tarns near Snowdon. By W. W. Watts, 



M.A., F.G.S.^ 



DURING a recent visit to North Wales, the writer has taken the 

 opportunity of examining a few of the tarns in the immediate 

 vicinity of Snowdon, including the two small lakes in Cwm Glas, 

 Glaslyn, and Llyn Llydaw. 



In the hollow of Cwm Glas there are two tiny tarns named 

 Ffynnon Freeh and Ffynnon Felen ; both lakes drain over a barrier 

 of rock, but in a rainy season the upper one appears to find a second 

 outlet over the long, low col to the east, so that in this state it 

 has the two outlets depicted on the six-inch map. The upper lake 

 appears to be a portion of a bending valley dammed at both ends by 

 scree and stream-debris, and thus compelled to find an escape over 

 the rocky side. The lower lake is confined in a rock-basin, as rock 

 occurs at its actual outlet and at every point where any former 

 outlet might have been possible. The lake is, however, so shallow 

 that its occurrence in a basin of rock is perhaps of little consequence. 



The neighbouring hollow of Cwm Dyli, as is well known, con- 

 tains three lakes, the highest being Glaslyn, the next Llyn Llydaw, 

 and the lowest Llyn Teyrn. Glaslyn is bounded on all sides by 

 live rock, except at and near its outlet. This exit is over moraine, 

 which, however, is evidently not very deep, for rock makes its 

 appearance just below, and in such a way as to almost compel belief 



1 Eead before Section C of the British Association at Ipswich, September, 1895. 



