308 J. F. BLAKE AND W. H. HTTDLESTON ON 



Section at the Cross Road to Cumnor. 



ft. in. 



1. Coralline brash in discontinuous beds, the fossils mostly broken, 



with Cidaris jlorigemma, C. Smithii 5 



2. Solid blue crystalline limestone, with irregular branching cavities, 



with Cidaris jlorigemma 2 



3. Soft brash in loose calcareous paste, full of broken fossils and 



occasional Thamnastrcece, Littorina muricata, Lima rigida, 

 Pecten vimineus, Escogyra nana, Cidaris Jlorigemma, C. Smithii, 

 Hemicidaris, sp. Towards the base it becomes more compact, 

 and is made up of prostrate Tkecosmilics and occasional Tham- 

 nastrcece 4 6 



4. Indurated limestone similar to above, the base a shell-bed with 



Littorina muricata, a clavellate Trigonia, Pecten vimineus, 

 Cidaris Smithii ••• 2 



5. Soft bluish sand, in which no fossils or doggers are seen 2 



There are three noticeable points about this quarry : — 1st, the 

 rubble overlying the representative of the Rag, a feature not before 

 noticed, but introducing us to a similar peculiarity at Headington, 

 to be presently described; 2nd, the massiveness of the crystal- 

 line Rag limestone, and its similarity to a bed of Calcareous Grit, 

 by which we might be misled but for the characteristic urchin ; it 

 is probably a highly altered coral-growth ; 3rd, the coral shell-bed 

 below, which we must plainly associate with the Rag rather than 

 with the shell-beds of Faringdon &c. The whole series presents 

 here a greater thickness than we have elsewhere seen on this 

 horizon throughout the range. 



6. North-east of Oxford. 



Here we have the last development of Corallian rocks before 

 their disappearance for many miles. Their character has already 

 been made known by Prof. Phillips and the Geological Survey, both 

 of whom have described the quarries at Headington. 



In the base of these quarries, as also in others, such as those near 

 the windmill on the Shotover road, we find the sands of the Lower 

 Calcareous Grit, with sometimes strong bands of stone, as in the 

 Littlemore railway- cutting, or large doggers with Ammonites vari- 

 costatus and other fossils. We have not met with the JVatica-bed of 

 Marcham in these quarries ; but the uppermost part of the sands 

 shows indications of that remarkable band at Bradley farm in 

 which Ammonites cordatus occurs in nodules of sharp calcareous 

 sand. 



That same fossil occurs here also in a similar matrix. There is 

 also at the top of the grit about eight inches of a pebbly bed, with 

 rolled oolite and quartz crystals, and containing Ostrea solitaria, AvU 

 cula exjpansa, Lima Iceviuscida, and Natica clytia. This probably 

 indicates some lapse of time during which deposits which are here 

 wanting were laid down elsewhere in the district. 



The continuation downwards of the Lower Calcareous Grit may 

 be observed in the road leading north from these quarries ; on 



