STRATIGRAPHICAL GEOLOGY. 437 



different from those of the Lower Silurian, and that the 

 Cambrian system was identical with the Lower Silurian. 

 Murchison made known this opinion for the first time in a 

 Presidential Address which he delivered at the Geological 

 Society. Sedgwick was deeply hurt, and immediately began 

 (1842 and 1843) a new investigation of Wales, in which he 

 was assisted by the palaeontologist Salter. In 1852, he upheld 

 the independence of the Cambrian series, contending that 

 under the Llandeilo of Murchison, which he recognised from 

 the identity in the fossils to be contemporaneous with the 

 Bala Beds and designated Upper Cambrian^ there was another 

 complex of strata about 10,000 feet in thickness. In this 

 complex, Sedgwick distinguished two main divisions, the 

 Festiniog and Bangor groups, with the subordinate members 

 Arenig flags and shales, Tremadoc slates, Lingula flags, Har- 

 lech grits and shales, and Llanberis shales. 



Murchison was not persuaded by Sedgwick's results, and 

 demanded a palaeontological foundation for the Cambrian 

 system. In the year 1854, a somewhat shortened and com- 

 pletely re-modelled edition of the Silurian System appeared 

 in octavo form, under the title Siluria. Murchison in this 

 edition treated the "Cambrian Series" merely as a local facies 

 of the Lower Silurian division, and set aside its claims to be 

 regarded as an independent system. Murchison's Siluria 

 begins with the oldest fossiliferous deposits in Wales (the 

 Longmynd group) and provides in ascending order a detailed 

 description of the Silurian, Devonian, Carboniferous, and 

 Permian systems in England, concluding with a comparative 

 account of the corresponding formations in the other parts of 

 Europe and North America. 



The members of the Geological Survey, to whom the in- 

 vestigation of Wales was entrusted, followed the views of 

 Murchison, the Cambrian system disappeared from the official 

 maps, and the colour for Silurian rocks was carried over the 

 whole of the area previously allotted to the Cambrian system. 

 Sedgwick, embittered by the want of recognition for his Cam- 

 brian system, published (1851-55) a large work on the 

 divisions and the fossils of the British Palaeozoic deposits, 

 and protested in strong terms against the views held by his 

 former friend and fellow-worker Murchison. He insisted 

 upon the independence of the Cambrian system, and wished 

 to limit the Silurian system to the Ludlow and Wenlock 



