THE CORALLIAN ROCKS OF ENGLAND. 321 



stones with reference to the ball-beds, which they immediately 

 overlie. This suboolitic phase of the Lower Calcareous series in a 

 northerly direction is important, as it tends to exhibit a link between 

 the oolite of the Lower Limestones presently to be described and 

 the somewhat abnormal development of its presumed equivalents at 

 Filey ; and, as will be seen in the sequel, it gives a means of more 

 accurately correlating the overlying grit(Filey-Brigg calcareous grit). 



In Oliver's Mount only the lower beds of the Lower Calcareous 

 Grit occur. These are quarried for building-stone, and contain but 

 few fossils. Avicula braamburiensis, Phil., Modiola bipartita, Sow., 

 Trigonia Bronnii, Ag.,and Rhynchonella lacunosa, Schlot., are quoted 

 from here. 



We must now follow the Corallian series into the interior ; and, 

 by way of introduction to its development in the inland portion of 

 our eastern or Scarborough district, we submit a section at the 

 mouth of Forge Valley (fig. 11). The gorge of the Derwent, which 

 passes completely through the Tabular Chain, debouches into the 

 vale at the village of Ayton. In so doing it cuts across the several 

 formations as they dip to the south ; and as the dip is more rapid 

 than the surface- slope, we continue to meet with higher beds in 

 that direction. The section is as follows, the thicknesses ascribed 

 to the beds being perhaps somewhat in excess : — 



A. Upper Limestones. ft. in. 



a. Coral Rag (Seavegate) 14 



b. Coralline oolite of Seamer (Seavegate) 25 



B. " Intermediate Series " (c of fig.) (above the White Quarry) 34 



C. Lower Limestones. 



d. Coralline oolite of Scarborough Castle (White Quarry) 33 



e. Upper portion of the basement or passage-beds (White Quarry 1 



and Greengate) I 30 



«'. Lower portion — ferruginous (Greengate) J 



Total thickness of beds between the top of the Lower Calca- 

 reous Grit proper and the top of the Coral Rag 136 



The above section has been constructed with the view of showing 

 the sequence of the Corallian Limestones ; and it may be deemed a 

 good introduction to the study of their development in Yorkshire, 

 being far more complete than any thing seen on the coast. The 

 lowest group of all {e) is a thick-bedded ferrugineo- calcareous grit, 

 quarried for building towards the 1ST.N.W. end of the section at 

 Greengate. It contains Lima Iceviuscula (peculiar coarsely-ribbed 

 form), Gervillia avkuloides (very large), Pecten Jibrosus, Rhyncho- 

 nella Thurmanni , Millericrinus echinatus, &c. The upper portion 

 (e) of the passage-beds of the Lower Limestones is thinner-bedded, 

 being generally an impure splintery limestone, with occasionally 

 oolitic structure. This upper portion has irregular shell-beds ; and 

 one may be noted at the foot of the White Quarry, containing nume- 

 rous Myacites, along with three very characteristic fossils, viz. Cylin- 

 drites elongatus, Gervillia aviculoides, and Rhynchonella Thurmanni. 

 J. G. S. No. 130. y . 



