1877.] Prof, Hughes, On the base of the Silurian system. G7 



Mmj 21, 1877. 



Pkof. Clerk Maxwell, F.R.S., President, in the chair. 



A communication was made to the Society by 



(1) Prof. T. McKenny Hughes, On the base of the Silurian 

 sjistem ; with note by Mr Marr, On the Phacopidae of the Lake 

 District. 



Professor Hughes read a pfiper, in which he attempted to fix 

 more exactly the base of the Silurian (Sedgwick) system in the 

 north of England, and traced the bearing of the results there 

 obtained upon the Welsh sections. At Austwick near Settle 

 the Basement Bed was a conglomerate resting on Upper Bala 

 Beds and covered by the Coniston Flags. At Crag Hill in the 

 upper part of Ribblesdale it was a brecciated limestone resting 

 immediately on the Coniston Limestone and succeeded by the 

 Coniston Flags. In neither of these cases had he detected any 

 traces of the Graptolithic Mud stones. Further north in the 

 Sedberffh district he found in several sections a similar consflo- 

 merate succeeded by shales which passed up into the Graptolithic 

 Mudstone, which, through the Pale Slates, passed up into the 

 Coniston Flags. Still further north in tSpengill, a tributary of 

 the Rothey, he found the Coniston Flags passing down through 

 Pale Slates into the Graptolithic Mudstone, in the upper part 

 of which was a thin limestone with fossils, to which he gave 

 the name of Spengill Limestone. The Graptolithic Mudstone 

 passed down into shale, at the base of which (just where the 

 conglomerate appears in the Sedbergh district) was a bed of 

 calcareous sandstone with fossils, which he thought was probably 

 the Basement Bed. 



Crossing over to the Lake District, in Skelgill, behind the 

 Low Wood Hotel, Windermere, the Coniston Flags passed down 

 through the Pale Slates into the Graptolithic Mudstone, at the 

 base of which was a pale calcareous sandy mudstone which he 

 took as the Basement Bed, and which rested on other pale slates. 

 These last passed down into, and he thought belonged to, the 

 Upper Bala series. Further west, in Ash Gill near Coniston, 

 the Coniston Flags pass down through pale slates into the 

 Graptolithic Mudstone, which in turn passes down into a knobbly 

 pyritous band representing the Basement Bed. This rests on 

 the Ash Gill slates, which pass down into, and seem to belong 

 to the Coniston Limestone series. 



