508 Prof. T. Sterry Kant — 0)% Cambrian and Silurian. 



whicli are not known in the otlier parts of Wales. The third area 

 of Lower Cambrian rocks is that already described at St. Davids in 

 Pembrokeshire,, about 100 miles to the south-west; and the fourth, 

 that of the Longmynd hills, about sixty miles to the south-east of 

 Snowdon. The rocks of the Longmynd, like those of the other 

 Lower Cambrian areas mentioned, consist principally of green and 

 purple sandstones with conglomerates, shales and some clay-slates. 

 They occasionally hold flakes of anthracite, and small portions of 

 mineral pitch exude from them in some localities. The only evidence 

 of animal life yet found in the rocks of the Longmynd are furnished 

 by worm-burrows, the obscure remains of a Crustacean (the Falceo- 

 pyge Bamsayi), and a form like Jlistiodet'ma. This latter organic 

 relic, with worm-burrows, and the fossils named Oldliamia, is found 

 on the coast of Ireland opposite Caernarvonshire, in the rocks of Bray 

 Head, which resemble lithologically the Harlech beds, and are 

 regarded as their equivalents. 



Still another area of the older rocks is that of the Malvern hills, 

 on the western flanks of which, as already mentioned, the Lingula- 

 flags are represented by about 500 feet of black shales with Olenus, 

 underlaid by 600 feet of greenish sandstones containing traces of 

 fucoids, with Serpulites and an Obolella. It is not improbable, as 

 suggested by Barrande and by Murchison, that these 1100 feet of 

 strata represent, in this region, the great mass of the Lingula-flags, 

 — and, we may add, perhaps the whole series of Lower Cambrian 

 strata, which in Caernarvonshire and Pembrokeshire underlie them ; 

 since these sandstones of Malvern, like those of St. Davids, rest 

 upon crystalline schists, and are in part made up of their ruins. 



These crystalline schists of Malvern, which are described by 

 Phillips as the oldest rocks in England, and by Dr. H. B. Holl are 

 conjectured to be Laurentian, seem from the description of their litho- 

 logical characters to resemble those of Caernarvon and Anglesea, 

 with which they are, by Murchison, regarded as identical. The 

 crystalline schists of these latter localities are, by Sedgwick, 

 described as hypozoic strata, below the base of the Cambrian. 

 Murchison however, in the first edition of his Siluria, adopted the 

 suggestion of De la Beche that they themselves were altered Cam- 

 brian strata. In fact they directly undeiiie the Llandeilo rocks, and 

 were apparently conceived by Murchison to represent the downward 

 continuation of these, upon which he had insisted. This opinion is 

 supported by ingenious arguments on the part of Eamsay. (Mem. 

 G-eol. Surv., vol. iii. part 2, passim.) I am however disposed to 

 regard them, with Sedgwick and Phillips, as of pre-Cambrian age, 

 and to compare them with the Huronian series of North America, 

 wliich occupies a similar geological horizon, and with which, as seen 

 in Northern Michigan, and in the Green Mountains, I have found the 

 rocks of Anglesea to offer remarkable lithological resemblances. 



It may here be noticed that the gold-bearing quartz veins in 

 North Wales are found in the Menevian beds, and also, according to 

 Selwyn, throughout the Lingula-flags. These fossiliferous strata at 

 the gold-mine near Dolgelly appear in direct contact with diorites 



