

>tt.1 NOMENCLATURE— CAMBRIAN. 239 



iii the revision of 1S.*'>S. It is also well to notice that tbe Cambrian of 

 L838 includes exactly the same, representative formations as Hnimous's 

 Taeonic System of 1842-1860, or the Cambrian and Lower Silurian 

 (Ordovician) as now known. 



In 1852 we find the Lower Cambrian divided into the Festiniog group 

 above and the Bangor below. The Bangor group is composed of the 

 Llanberris slates aud Harlech grits; and the Festiniog group of the 

 Lingula flags, Tremadoc slates, and Arenig slates arid porphyry, the 

 whole having a thickness of 10,000 feet. The Upper Cambrian includes 

 the Bala group, which was divided into the Lower and Upper Bala, 

 with a thickness of 8,000 feet. Above this the Caradoc sandstone, 

 limestone, and shale of the Silurian occur with a thickness of 1,500 

 feet, 1 



In the paper on the Caradoc sandstone of Shropshire, by Messrs. J. 

 W. Salter and W. T. Aveliue, it is stated that the fossils of the supposed 

 typical Caradoc saudstone are identical in species, and in association 

 and proportionate numbers of the prevailing species, with those of the 

 Bala group ; and there is no admixture of other or new forms, or of 

 those characteristic of higher parts of the system. 2 By priority of 

 definition and description, the Llandeilo and Caradoc beds belong to 

 Murchison's Silurian system ; and the Bala series of Sedgwick are 

 strati graphically and paleontologically the equivalents of the Llandeilo 

 and Caradoc series. They were fairly removed from the Cambrian 

 system by the work of Messrs. Murchison, Sedgwick, and Salter; and 

 in 1854 the Cambrian system included of the original Cambrian the 

 middle member only, the lower division having been removed by Prof. 

 Sedgwick in 1838. The distinguished founder of the Cambrian system 

 did not admit the exclusion of the Bala series from the Cambrian, but 

 with all the facts assembled, as in a recent paper by Prof. J. D. Dana, 3 1 

 . think we are compelled to restrict the Cambrian to the original middle 

 division. 



The last tabulation given by Prof. Sedgwick of his Cambrian system 

 appeared in the preface of Mr. J. W. Salter's Catalogue of Cambrian 

 and Silurian Fossils in 1873, as follows: 4 



S Upper Bala. 

 Middle Bala. 

 Lower Bala, 

 f Arenig or Skiddaw. 

 Tremadoc. 

 Ffestiniog. 

 ^Meiievian. 

 ( Harlech. 



Lower J Bail S or - 



^Longmynd. 



[^Llanberris. 



Cambrian : < 



Middle 



1 On the classification and nomenclature of the Lower Paleozoic rocks of England and Wales- 

 Quart Jour. Gcol. Soc, London, vol. 8, 1852, p. 147. 



2 On the "Caradoc Sandstone" of Shropshire. Quart. Jour. Geol. Soc, London, vol. 10, 1853, p. 63. 



dgwick and Murchison ; Cambrian aud Silurian ; Am. Jour. Sci., 3d ser., vol. 39, 1890, pp. 107-180. 

 '(On the classification of the Cambrian rocks). " Preface to a Catalogue of the Collection of Cum. 

 biian and Silurian fossils contained in the Geological Museum of the University of Cambridge," by J- 

 W. Salter, 1873, p. xv. 



