78 CAMBRIAN. 



opinion, mark an unconformity. The flaggy beds exhibit little or 

 no cleavage. 



The Skiddaw Slates may be divided as follows, according to I\Ir. 

 Ward : '— 



Skiddaw Slate proper (black clay-slate _ ((Llanvirn Series) and 



of Skiddaw). ~ "(Arenig Slates. 



Coarse Grit. - = Arenig Grit. 



Black iron-stained slates. = Tremadoc Slates. 



Thick-bedded sandy and gritty series (of _ j • i tti c • 



Grasmoor and Whiteside). " l^mgula 1- lag beries. 



The beds are developed, as their name implies, on Skiddaw, also 

 on Saddleback, Cawsey Pike, Grasmoor Fells, near Egremont, 

 Cockermouth, Loweswater, Buttermere, and Crummock Lake: they 

 form the mountain of Black Combe, etc., and they occur over a 

 large area in the Isle of Man.^ They are seen also at the foot of 

 the Cross Fell escarpment. (See Fig. 25.) They attain a thick- 

 ness of from 10,000 to 12,000 feet, but nowhere is the base ex- 

 hibited. 



The Graptolites discovered by Joseph Graham, Ruthven, and 

 Harkness, form the most remarkable fossils of the Skiddaw Slates ; 

 these include the genera Dichograptus, Didymograptus, Diplograptns, 

 l^etragraptus, and Fhyllograplus, and Graptolites Sagittarius. 



A Phyllopod {Caryocaris Wrightii) and some Trilobites occur, 

 the latter including Phacops Nicholsimi (which has been taken to 

 indicate a zone), jEglina binodosa, Agnostus Morei, etc.; also Lingula 

 brt'vis ; and Palceochorda major, Scolites, and other markings like 

 Annelide burrows. Fossils may be found in many places near 

 Keswick, at Outerside, Barif, etc., and in the 'screes' on the slopes 

 of Black Combe, etc. Our knowledge of the fauna is largely owing 

 to the researches of Prof. R. Harkness and Prof. H. A. Nicholson,* 

 and especially to Mr. W. Kinsey Dover, Mr. J. Postlethwaite, and 

 others residing in the district.* 



The rocks indicate shallow-water and shore conditions, with 

 land most likely in the west, according to Mr. Ward. Some pos- 

 sible plant-remains have been identified under the name of Butho- 

 trephis, Eophyton, and Chondrites. 



INIr. Ward has remarked, that as we approach the granite area of 

 Skiddaw, the slate becomes spotty, crystals of Chiastolite appear, 

 and the rock becomes a Chiastolite Slate.* This passes into a 

 harder, more thickly-bedded, foliated and massive rock. Spotted 

 (or Andalusite) Schist ; and this again into a kind of Mica Schist 

 of generally a grey or brown colour, which occurs immediately 

 around the granite.^ 



1 G. Mag. 1879, pp. 50, 122 ; 1S80, p. i. 



2 g. J. xxii. 488. 



'■'• Q. J. xix. 313 ; xxiv. 125 ; G. Mag. 1869, p. 49S. 



* Trans. Cumberland Assoc. No. x. p. 71. 



5 Noticed by Sedgwick, Q. J. ii. 106. 



^ Geology of the N, Part of the English Lake District, p 9. 



