THE CORALLIAN ROCKS OF ENGLAND. 309 



the slope of the hill a considerable amount of loose yellow sand is 

 seen, with occasional hard bands with Ammonites perarmatus. 



Overlying the Lower Calcareous Grit there are several different 

 types of rock in this neighbourhood. In the great Headington 

 quarries we have no less than three series of beds, as indicated in 

 the following section : — 



Section of Headington Quarries. 



ft. in. 



1. False-bedded comminuted shell-limestone, seen better in the 



quarries at Shotover at a higher level here 16 



2. Irregular Coral Rag with Thecosmilice, passing into and alter- 



nating with the beds above 10-17 



3. Semi-oolitic shell-bed with Cidaris florigemma 7 



4. Pebbly bed and layers of nodules with Ammonites cordatus 8 



5. Sands of the Lower Calcareous Grit. 



The ' shell-bed, No. 3, is a very interesting one from its abun- 

 dance of fossils, among which we notice Ammonites plicatilis, Pha- 

 sianella striata, Natica clytia, Astarte ovata, Gervillia aviculoides, 

 Perna mytiloides, Corbicella Icevis, Myoconcha Scemanni, Lima lozvi- 

 uscida, Pecten lens, and P. vimineus, as well as Cidaris florigemma. 

 It is the presence of this last fossil that makes us associate this with 

 the Coral Rag, as a bed not seen before except near Cumnor, rather 

 than consider it the equivalent of the shell-beds at Faringdon. 

 The Phasianella striata gives the same indication, though it occurs 

 also at High worth. It is a feature more common in Yorkshire than 

 in the south of England to have such a shell-bed associated with 

 the Rag. In one of the quarries this bed contains a mass of corals ; 

 and in another place it is separated by a layer of sand from the over- 

 lying Rag. The stone is mostly composed of broken shells and 

 impure limestone, but occasionally shows oolitic structure. 



The Coral Rag, No. 2, is almost entirely composed of Thecosmilice, 

 very few Thamnastrcece being observed. It is very irregular, and 

 cannot be traced far continuously. It appears to be false-bedded, 

 probably from growing on a false-bedded basis ; sometimes it is 

 quite soft, like loose calc tuff; at others it hardens into lenticular 

 masses of solid rock with fewer corals — a very typical Thecosmilian 

 Rag. We noted Pleurotomaria reticulata, Pecten vimineus, Lima 

 ellijotica, and Ostrea solitaria, besides the inevitable urchin. 



This Rag becomes in parts undistingnishable from the false- 

 bedded limestone, No. 1, which is finally substituted for and overlies 

 it. This is seen in one of the quarries on the south of the general 

 quarry ; so that the relation of the two rocks is undoubted. This 

 soft limestone, however, is better seen in a quarry higher up the 

 hill, where it is quarried beneath the Kimmeridge Clay, which, as 

 noticed by Phillips, lies on an eroded surface. The limestone is com- 

 posed of comminuted fragments of shells — a very unfavourable con- 

 dition for holding any recognizable fossils ; but it appears to contain 

 the spines of Cidaris florigemma. About 10 feet are seen in one 

 quarry, and 10 feet more in a lower one ; but there are reported to 



