Reviews — Murchison^s *' SiluriaJ^ 81 



The next overlying stage of deposits is represented by the succes- 

 sion of flagstones, grits, and fossiliferous schists, 5,000 feet (?) thick, 

 long known as the '' Lingula-flags;" but as their chief '' Lingulae " 

 are Lingulellce, and as Lingidce abound also elsewhere, Murchison 

 refers to them as '*' Primordial Silurian," after Barrande's name of 

 " Primordial Zone." They flank both the Longmynd and the 

 Malvern Hills on their western sides, comprising the " Holybush 

 Sandstone" and Olenus-shale of the Malverns ; they enter into the 

 constitution both of Snowdon and of Cader Idris, on either side of the 

 Harlech anticline ; and they form the two great corresponding pro- 

 montories of Caernarvon and Pembrokeshire. " This great series 

 of Lingula-flags, so well developed in Wales, is the zone which, in 

 Bohemia, through the enlightened researches of Mr. Barrande, has 

 proved to be the basis of all Silurian life, and which therefore 

 received from him the name of 'Primordial.' It is, indeed, clear 

 that the fauna of this zone merits all the importance attached to it 

 by its eminent founder, since we have now ascertained that, such as 

 he has described it, the group exists in America, Scandinavia, 

 Belgium, and Spain, as well as in the British Isles and Bohemia " 

 (p. 47). This "Primordial Zone " is grouped by Sedgwick, Salter, 

 and Lyell as the upper portion of the Cambrian system ; but with 

 Murchison's " Cambrian " these Lingulella-flags have nothing in 

 common, except that one small Lingula {L. ferruginea, var. ovalis), 

 and one Trilobite (Palceopyge Kamsayi) have been found in the latter, 

 showing that the life of the Lower Paleeozoic era had then already 

 commenced. 



The Llandeilo formation, very rich in Graptolites, Trilobites, and 

 other fossils, and upwards of 5,000 feet thick (including its inter- 

 calated lavas and ash-beds of contemporaneous volcanic origin), next 

 succeeds, forming a large part of Wales, and well represented 

 abroad. The lower portion of this series has been divided off by 

 other systematists as the " Tremadoc Slates," but Sir Eoderick re- 

 gards the latter as real passage-beds between the Primordial Zone and 

 the Llandeilo flags, and inseparable in classification. 



The Caradoc or Caradoc-Bala beds (4,000 feet in Shropshire, and 

 thickened with upwards of 3,000 feet of contemporaneous volcanic 

 rock in North Wales) are next described, with their many Brachio- 

 pods, Trilobites, etc. Lying on the Llandeilo flags (and, indeed, 

 formed in the shallowing sea, which at first, when deeper, origi- 

 nated these latter shales and flagstones), the Caradoc beds cap 

 Snowdon, and largely participate in forming the northern, central, 

 and south-western districts of Wales and the border-counties in- 

 cluded in Murchison's original " Siluria," or land of the old British 

 Silures of Caractacus. This Silurian formation being shore-beds 

 and sandy towards the east, its numerous shells have left only 

 casts and moulds in the " Caradoc Sandstone ;" but the more muddy 

 beds of the western and northern parts of the area have preserved 

 the calcareous matter of the shells and corals more perfectly in the 

 " Bala Limestone." Such a difference of character, further modified 

 by the intercalation of volcanic ash-beds, was originally a hindrance 



VOL. V. — NO. XLIV. 6 



