318 GEOLOGY OF THE BEISTOL COAL-FIELD. 



LowEE Caebonifeeotjs Shiles. 



The figures within [ ] denote the number of feet from the commencement 

 of Section. 



1. — [360]. — Pirst bed witli carbonate of lime in any quantity, 

 and one foot thick. 



2. — [385]. — Athyris Roysii bed of very aluminous limestone 2 

 feet in thickness. Every part of the bed is crowded with fossils. 

 The most characteristic are : — Athyris Roysii (Dav.,) Spirifera 

 rhomloidea (Phill.,) Ret%ia radialis (Phill.) 



[400]. — Hard dark limestone 3 inches thick, resting on 12 inches 

 of yellow marl. The stone is full of minute shells, probably the 

 young of Naticopsis and Rissoa and Cytheridce. 



3. — [408]. — Sanguinolites shales. Greenish arenaceous shales, 

 very fissile and with abundant and good casts of Sanguinolites 

 augustata (Phill.) and S. complanata (Phill). A good spot for 

 collecting them is a few yards in the wood. 



4 . — [41 3] . — Modiola shales. This is probably the most important 

 bed of the Lower shales, for many of the fossils are identical with 

 those of the Marwood, Coomhola, Moj^ola, and the Scotch Coal 

 Measures, so that they go far to support the idea of some of the 

 Upper Devonian belonging rather to the Carboniferous period. 

 Another fact is that the whole of the beds are full of grass-like 

 weeds similar to those of shallow sea shores, or rather to land at a 

 low altitude which is periodically subject to the influence of high 

 tides. Mixed with these plants are immense masses of the cast off 

 valves of entomostraca. 



The late Professor Jukes said, ''If the Coomhola grits be classed 

 with the Carboniferous series, the so-ealled Upper Devonian of 

 Devonshire must be classed with the Marwood group as Carbonif- 

 erous ; and if classed with the Devonian, they must be set aside as 

 a distinct sub-group." 



The following is a comparative table of these ''Modiola" fossils, 

 which appear to render the above mentioned idea conclusive. 



