HUGHES : IXGLEBOROUGH. 
341 
Cheirurus bimucronatus Murch. 
Cybele verrucosa Dalm. 
Illcenus bowmanni Salter. 
Phacops ? obtusicaudatus Salt. 
Discina. 
Leptosna sericea Sow. 
L. transversalis Wahl. 
Lingula ovata M'Coy. 
Or this ActonicB Sow. 
Orthis biforata Schlotli 
Orthis calligramma Dalm. 
Orthis elegantula Dalm. 
Orthis flabellulum Sow. 
Orthis vespertilio Sow. 
Rhynchonella. 
Strophomena grandis Sow. 
Modiolopsis antiqua Sow. 
Murchisonia. 
The grey crystalline limestone (e) is taken for the present at 
any rate as the basement bed of the Silurian, and will be described 
by-and-by. 
The Coniston Limestone and Shale are again seen a short distance 
north-east of Horton-in-Ribblesdale. The stream issuing from the 
Mountain Limestone in Dow Gill, about 100 yards below its source, 
has cut through the basement beds and exposed the green slates 
dipping at a high angle a little west of south. They are followed in 
apparently conformable succession by the Coniston Limestone and 
Shale which are here highly fossiliferous. About 150 yards down 
stream they begin to turn up to a fault thus lying in a broken synclinal. 
SUMMARY. 
The Arenig Series. 
This forms the base of the group, and in the typical areas of North 
Wales and the Lake District consists of black shales, here and there 
more sandy or streaked with sandy layers. It has a very distinctive 
fauna, with indications in the upper part of the commencement of 
