C. LAP WORTH ON THE MOFFAT SERIES. 253 



our great divisional line their place is taken by the bilateral genera 

 Dicranograptus (Hall) and Dicellograptus (Hopk.) of the very dis- 

 tinct family of the Dicranograptidae. 



The beds above this separating line, which thus compose the 

 first natural division of the Moffat Series as here displayed, I 

 distinguish by the title of the Birkhill Shales, after the name of 

 the watershed in the immediate neighbourhood. 



(II.) Second or Hartfell Division. 



A single glance at the strata that underlie the Birkhill Shales of 

 the Main Cliff, and thus constitute the second provisional division of 

 the Moffat Series, is sufficient to assure the geologist of the fact 

 that, like the beds of our first division, they fall naturally into two 

 very distinct lithological groups. The higher of these groups is 

 made up of 50 feet of green, grey, and brown shales and mudstones, 

 with a few intercalated lines of black shale, and the lower of 45 feet 

 of hard black slaty shales and flagstone. 



The upper group of pale mudstones is, again, clearly formed of two 

 distinct subdivisions, viz. : — 



(a) A superior zone of soft green, yellow, white, and black mud- 

 stones. The black lines in the mudstones swarm with badly pre- 

 served examples of Dicellograptus anceps (Nicholson). 



(b) An inferior zone of pale greenish-grey flaggy mudstones, 

 about 30 feet in thickness, totally devoid of fossils except in a small 

 line about 2 inches in depth near its base. 



The inferior, or black-shale group may most conveniently be 

 regarded as composed of three zones : — 



(a) The highest zone is formed of hard black slaty shales, varied 

 by thin cream-coloured seams of white mudstone. Fossils are 

 abundant, the most characteristic being the peculiar Pleurograptus 

 linearis (Carr.). 



(b) The middle zone is formed of similar hard black shales, but it 

 includes several bands of tough siliceous black flags, about 2 inches 

 in thickness, while the white seams of the zone last described are 

 absent throughout. 



The characteristic fossil is Dicranograptus Clingani (Carr.). 



(c) The lowest zone is composed of dark greyish-black flagstones 

 and shales totally destitute of fossils except in three or four thin 

 seams, where they occur in a state of exquisite preservation. 



The most abundant species is Climacograptus Wilsoni (Lapw.). 



This second division of the Moffat Series is denominated the 

 Hartfell Shales, after the locality where its beds are most perfectly 

 exhibited, which will be described in detail in the next portion of 

 this paper. 



(III.) Third or Glenkiln Division. 



The Birkhill and Hartfell Shales include the whole of the beds 

 exposed in the Main Cliff', with the exception of a narrow wedge of 

 dark flagstones, 15 feet in thickness, visible at its south-west corner. 



