132 



SCIENTIFIC SURVEY OF BLACKPOOL AND DISTRICT 



Silurian. 



The Silurian strata consist of slates and sandstones of which some details 

 are given in the table below. 



The Skelgill Beds, at the base, rest conformably on the Ashgill Shales, 

 though there is a marked change in hthology near the junction. There are 

 eleven zones in the Skelgill Beds and two in the Browgill Beds, characterised by 

 different species of Monograptus, and the trilobites Ecrinurus punctatus, 

 Phacops glaber, and Acidaspis erinaceus. 



The Silurian Strata. 



Downton 

 Series 



Thickness 

 in feet. 



Absent. 



Ludlow 

 Series 



Wenlock 

 Series 



Llandovery 

 Series 



Kirkby Moor flags ; grey-green flags with some 

 gritty bands : much mica : some soft calcareous 

 bands rich in brachiopods and starfish .... 



Banmsdale Slates ; leaden-grey sandy mudstones 

 with thin bands of greenish sandstone and 

 occasional grits : much jointed and cleaved : 

 fossils few but include Monograptus leintwardi- 

 nertsis 



Coniston Grits ; fairly coarse grits with a band of 

 flaggy mudstone (' sheer-bate flags ') near 

 middle : few fossils 



Upper Coniston Flags or Coldwell Beds : olive- 

 weathering, grey flags with some grit : grapto- 

 lites of M.colonus type : coarse grit at base with 

 Cardiola interrupt a and Phacops obtusicaudatus 



Lower Coniston or Brathay Flags ; blue-grey 

 laminated mudstone with gritty partings : have 

 been used for roofing tiles and flagstones : 

 fossils not abundant but include M.priodon and 

 Cyrtograptus murchisoni 



Stockdale Shales ; Browgill Beds, 200 feet greenish 

 shales with dark graptohtic shales and some 

 greenish grit : Cyrtograptus appears. Skelgill 

 Beds ; 50 feet black graptolitic shales with thin, 

 pale bands of shale 



Old Red Sandstone. 



1,500 



5,000 (?) 



4,000 



1,500 



1,000 



250 



Deposition appears to have ceased for a while in the Lake District after the 

 laying down of the Kirkby Moor Flags. Earth-movements on a large scale 

 took place, and the rocks were folded, uplifted and denuded, and were invaded 

 by large masses of igneous material. The major anticline, recognisable amidst 

 innumerable folds, runs east-north-east through Skiddaw and is responsible 

 for the present distribution of the main outcrops of the Borrowdale Volcanic 

 Series. 



