THE LAKES OF SNOWDONIA AND EASTERN CARNARVONSHIRE. 423 



glacial phenomena of this region were so fully and admirably described. While holding 

 that many of the lakes owe their origin entirely to ice-erosion, he allows that some of 

 them are, partially at least, dammed-up by moraines. 



Mr W. W. Watts contributed "Notes on some Tarns near Snowdon" to the GeoJ. 

 Mag., 1895 (p. 565). The tarns dealt with are Ffynnon Freeh and Ffynnon Felen in 

 Cwm Glas, and Glaslyn and Llydaw in Cwm Dyli. He concludes that the lower lake in 

 Cwm Glas is certainly confined in a rock-basin, and that Glaslyn and Llydaw, unless 

 much shallower than is generally supposed to be the case, also lie in rock-basins. 



Some of the lakes of Eastern Carnarvonshire are discussed by Mr Brend in a 

 short paper which appeared in the Geol. Mag., 1897 (p. 404). He took soundings in a 

 few of them, and figures are given indicating the greatest depth in feet obtained in each 

 case. He concludes that in most of them it is impossible to exclude the possibility of 

 a drift-dam; but, judging from the surroundings, Crafnant almost certainly lies in a 

 rock-basin. 



Messrs Marr and Adie are the joint authors of a paper on " The Lakes of Snow- 

 don," already referred to. They discuss the origin of both the lower valley-lakes and of 

 the upland tarns of Snowdon. The conclusion arrived at is that in no case can there be 

 found evidence sufficient to prove the existence of a rock-basin, and that all probably 

 owe their origin to the filling up of a depression by drift. 



Mr J. R. Dakyns published a paper in the Geol. Mag., 1900 (p. 58), on " Some 

 Snowdon Tarns," in which the views put forth by Messrs Marr and Adie as to their 

 mode of origin are stoutly controverted. 



The discussion carried on with regard to the mode of origin of the Snowdonian 

 lakes has been hampered by the lack of positive knowledge as to their depths. Argu- 

 ments are sometimes advanced on the assumption that a lake has only a depth of a 

 certain number of feet. And Messrs Marr and Adie in their paper express a strong 

 desire that accurate soundings of these lakes should be made. 



III. The Orographical Features of the District. 



The lakes dealt with in this memoir are all situated in the mountainous region of 

 Carnarvonshire. Within this area occur the highest mountains in Wales. The general 

 distribution of the lakes and the physical features of the region are shown in the 

 contoured map appended to the memoir (Plate III.). The height of the land is 

 indicated, and the lakes dealt with in this memoir are coloured blue. The district 

 comprises the Snowdon region and the part of Carnarvonshire lying to the east 

 of this region. It is unequalled in Wales for the height of its mountains and the 

 wildness of its scenery. A glance at the map will show that within this district we 

 can distinguish three mountain-tracts, which, in the course of time, have become 

 separated by valleys trending from south-east to north-west. To the west the great 



