XIII.] GEOGNOSY OF THE APPALACHIANS. 267 



Cambrian. To these succeed the Bala or Upper Cambrian, 

 the equivalent of the Llandeilo and Caradoc rocks, to 

 which Murchison gave the name of Lower Silurian. He at 

 first claimed the Llandeilo as the base of his Silurian system, 

 but subsequently endeavored to extend it downwards so as to 

 include, under the name of Primordial Silurian, the Middle 

 Cambrian of Sedgwick. To this Lyell objected, and while 

 conceding to Murchison the Upper Cambrian as Lower Silu- 

 rian, gave to the middle division of Sedgwick's series the 

 name of Upper Cambrian. Hicks in a recent paper (1873) 

 has adopted a similar compromise, including, however, in the 

 Lower Silurian the Arenig group, and making the Tremadoc 

 the upper member of the Upper Cambrian. For a discussion 

 of the relations of Cambrian and Silurian the reader is re- 

 ferred to Essay XY. in this volume.] The same classification 

 is now adopted by Linarsson, in Sweden, where, in Westro- 

 gothia, the Cambrian rocks (resting unconformably on the 

 crystalline schists to be noticed further on) are overlaid con- 

 formably by the orthoceratite-limestones, which are by him 

 regarded as forming the base of the Silurian, and as the equiva- 

 lent of the Llandeilo rocks of Wales. The total thickness of 

 these lower rocks in Sweden, including the representatives 

 of the Lingula flags, the Menevian beds, and an underlying 

 fucoidal (Eophyton) sandstone, is only three hundred feet, 

 while the first two divisions in Wales have a thickness of five 

 to six thousand, and the Harlech grits and Llanberis slates 

 (including the Welsh roofing-slates beneath) amount to eight 

 thousand feet additional. Eecent researches show that these 

 lower rocks in Wales contain an abundant fauna, extending 

 downward some 2,800 feet from the Menevian to the very 

 base of strata regarded as the representatives of the Harlech 

 grits. The brachiopoda of the Harlech beds appear identical 

 with those of the Menevian, but new species of Conocephalites, 

 Microdiscus, and Paradoxides are met with, besides a new 

 genus, Plutonia, allied to the last mentioned.* [The Upper 



* Hicks, Geol. Mag., V. 306 ; and Kep. Brit. Assoc., 1868, p. 69 ; also 

 Harkness and Hicks in Nature, Proc. Geol. Soc., May 10, 1871. 



