18 Transactions of the 



bed, he found a bed coutaining marine shells of the species 

 Modiola Macadami, and other fossils. These beds were exposed 

 on the old line of railway to Avonmoiith. 



The new railway is being cut above the old one, and an excel- 

 lent section is afforded. Mr Williams' list is of no use for this 

 section, as it is impossible to identify his beds. I therefore made 

 the following list with careful measurements, and in so doing 

 found fossils in many beds not previously described as fossili- 

 ferous. 



Mr Sanders, who made the well-known map of this district, 

 went on the principle that the Lower Limestone shales extend as 

 far downward as there are Carboniferous fossils to be found, and 

 he called the beds below Mr Williams' bed Passage beds, leaving 

 it uncertain whether they belonged to the Old Eed Sandstone 

 formation or to the Carboniferous. The result, then, of this 

 examination has been to draw the line sliarper between the two 

 formations, and to get rid of some of this debatable land. The 

 Modiola has been found as far down as 104 feet below the bone 

 bed, leaving only about 20 feet to be disputed. It is possible that 

 a closer examination will still further diminish the gap. 



There is another question, however, of great interest connected 

 with these beds. In Ireland the thickness of the beds between 

 the Carboniferous Limestone and the Old Red Sandstone, instead 

 of being only 500 feet as here, amounts to 5000 feet, and must 

 have taken thousands of years to deposit. They are divisible into 

 two main groups of 2000 and 3000 feet respectively, characterised 

 by their own peculiar fossils. 



The lower group, 3000 feet thick, is called the Coomhola grits. 



At Marwood, near Barnstaple, North Devon, are found sand- 

 stones, yellow, brown, and red, with plants and marine shells, 

 some of which are common to the Carboniferous rocks, others are 

 Devonian. It has been disputed whether they should be reckoned 

 Carboniferous or Devonian. 



Mr Stoddart has shown (Report of British Association for 1864) 

 that these Clifton beds correspond with the Coomhola grits, and 

 he maintains that they also c orrespond with the Marwood beds, 

 because a certain number of the fossils are identical. By increas- 

 ing the list of fossils, we may work out this parallelism in greater 

 detail. At present the Marwood sandstones are classified as 

 Devonian, not as Carboniferous ; whilst the Coomhola grits are 

 considered to be Carboniferous. The question also arises, how far 

 the lower sandy portion of these beds corresponds with the Glen- 

 gariff grits and other beds in Ireland which lie below the Coom- 

 hola grits, and which are reckoned as Devonian. Great interest, 

 therefore, attaches to the fossils and beds in the following list. 



