132 STRATIGRAPHICAL GEOLOGY 



green or purple colour. They are the " Green Slate and Porphyry 

 Group " of Sedgwick, afterwards called the Borrowdale Series. 

 Their total thickness is estimated to be 12,000 feet, but not all of 

 this is of Llandilo age ; as above stated the lower part is evidently 

 of Llanvirnian date, the central part must be Llandilian, and the 

 highest part may be of Bala age ; for in the Lake District the 

 volcanic series is directly succeeded by the Coniston limestone, but 

 in the Cross Fell inlier there are stratified beds containing Bala 

 fossils between the limestone and the highest rhyolite of that area. 

 Bala Series. The thickness of the stratified portion of this 

 series, even including those of Roman Fell, is much less than the 

 corresponding beds in Wales (i.e. about 300 feet), but a regular 

 zonal succession can be made out. The series has been subdivided 

 by Dr. Marr 15 as follows : 



Coniston area. Cross Fell area. 



Ashgillian / Shales - .... i Ashgill shales. 



Sleddale Beds 

 Roman Fell Group Rhyolite. Corona Beds. 



The " Corona Beds " are a set of calcareous shales, limestones, 

 and ash beds, about 100 feet in thickness, and they contain many 

 brachiopods, such as Trematis corona, Linyula tennigranulata, 

 Orthis testudinaria. The limestones consist largely of the tests of 

 a small Crustacean called Beyrichia. 



The Apple thwaite limestone consists of calcareous shales with 

 bands of limestone and a peculiar bed of white horny limestone at 

 the top. Overlying this is a bed of grey limestone about 5 feet 

 thick which contains the fauna of the Rhiwlas and Sholeshook 

 limestones, i.e. many Cystidean Echinoderms with Staurocephalus 

 clavifrons, Phacops apiculatus, and Orthoceras vayans. 



The limestones are succeeded by dark blue and grey shales 

 which yield many of the same fossils that occur at similar horizons 

 in North Wales. 



4. Scotland 



The southern uplands of Scotland are largely composed of 

 Ordovician and Silurian rocks folded together into a number of 

 anticlinal and synclinal folds, each fold having its subsidiary 

 plications, so that the country has a complicated structure, and can 

 only be successfully mapped by careful attention to fossils. The 

 older views about this region were mistaken because the fossils 

 were not sufficiently studied, and because it was supposed that 



