298 THE CANADIAN NATURALIST. [Vol. vi. 



and finally to assert that these three independent faunas '-form 

 by their union an indivisible triad which is the Silurian system." 

 [Bui. Soc. Geol. de Fr. II, xvi, 529-545.] Already, in 1852, in 

 his magnificent work on the Silurian System of Bohemia, Bar- 

 rande had given to the strata characterized by his first fauna 

 the name of Primordial Silurian. It is difiicult to assign any 

 just reason for thus annexing to the Silurian, — already augment- 

 ed by the whole Upper Cambrian or Bala group of Sedgwick, 

 (Llandeilo and Caradoc) — a great series of fossiliferous rocks 

 lying below the base of the Llandeilo, and unsuspected by the 

 author of the Silurian system ; who persistently claimed the Llan- 

 deilo beds, with their characteristic second fauna, as marking the 

 dawn of organic life. 



Up to this time the primordial paleozoic fauna of Bohemia and 

 of Scandinavia was, as we have said, unknown in Great Britain. 

 The few org;inic remains mentioned by Sedgwick in 1835 as 

 occurring in the region occupied by his Lower and Middle Cam- 

 brian, on Snowdon, were found to belong to Bala beds, which 

 there rest upon the older rocks: nor was it until 1845 that Mr. 

 Davis found in the Middle Cambrian remains of Lingula. In 

 1846. Sedgwick, in company with Mr. Davis, re-examined these 

 rocks, and in December of the same year described the Lingula- 

 beds as overlaid by the Trcmadoc slates and occupying a well- 

 defined horizon in Caernarvon and Merionethshire, beneath the 

 great mass of the Upper Cambrian rocks. [Geol. Jour. II, 75, 

 III, 139.] Sedgwick, at the same time, noticed about this 

 horizon certain graptolites and an Asaphus, which were supposed 

 to belong to the Tremadoc slates, but have since been declared 

 by Salter to pertain to the Arenig or Lower Llandeilo beds, the 

 base of the Upper Cambrian. [Mem. Geol. Sur. Ill, 257, and 

 Decade II.] 



This discovery of the Lingula-flags, as they were then named, 

 and the fixing by Sedgwick of their geological horizon, was at 

 once followed by a cireful examination of them by the Govern- 

 ment surveyors, and in 1847, Sclwyn detected in the Lingula- 

 flags, near Dolgelly, in Merionethshire, the remains of two 

 crustacean forms, the one a phyllopod, which has received the 

 name of IJjjmenocaiis verm {can da. Salter, and the other a trilo- 

 bite which was described by Salter in 1849 as Ohnus micrurus. 

 [Geol. Survey, Decade IL] A species of Para doxides, apparently 

 identical with P. ForMammeri of Sweden, was also about this 



