306 J. F. BLAKE AND W. H. HUDLESXON ON 



Section in Marcham Field, South Quarry. 



ft. in. 



1. Thin-splitting, rough-bedded blue limestone with Thecosmilia ... 2 6 



2. Rubbly Coral Rag in small pieces ; Thecosmilia, Cidaris florigemma 2 6 



3. Soft irregular thin-bedded limestone amalgamating with the 



Coral Rag aboye ; Ger vittia a viculoides 3 in. to 8 



4. Oolite and oolitic brash, variable ; Ammonites plicatilis 1 8 



5. Trigo'iiia-bed, composed of large specimens of Irigonia perlata, 



particularly towards the base ; contains Pleurotomaria reticulata, 

 Quenstedtia lesvigata, Pema mytiloides, Lucina Moreana, Opis 

 Phillipsi, Lithodomus inclusus, Gervillia avieuloides, &c 1 



6. Loose yellow sands, sometimes false-laminated, with thin layers 



of clay and abundance of Ostrca gregaria and Exogyra nana at 

 the top, and flat calcareous balls and Lydian stones towards 

 the base 1 ft. to 2 



7- Solid blue false-bedded calcareous grit, having the top full of 

 Natica marchamensis • contains also Chemnitzia abbreviata and 

 Ceritkium muricatum, var 8 in. to 1 



8. Loose sand, holds up water. 



This magnificent quarry gives us the whole sequence, and is a 

 splendid illustration of the Rag supported on a calcareous basis 

 There is no difficulty in correlating it with our other sections ; and 

 its fossil contents give it an interest of its own, the Trigonia-hed 

 being, like the corresponding beds elsewhere, the chief repository 

 of them. 



Very close to this quarry, but nearer to the Abingdon road, is 

 another, into which the lower beds may be traced one by one ; but 

 above the I'rigonia-bed we have the shelly sand of the Lamb-Inn 

 Quarry again, and the same erosion, though not so marked, with a 

 bed of rolled oolitic fragments ; but we see no Coral Rag. This 

 quarry is mapped as being in Lower Calcareous Grit. 



Now we notice that in these quarries we have two types of rock 

 overlying the shell-beds : in some places there are rubbly oolites, 

 and in others sands. In the former we generally see the Rag 

 resting on the top ; but in the latter the Rag is mostly driven out ; 

 so that these sandy areas are to a certain extent alternative with 

 those with Rag developments, and may, perhaps, have been so in 

 their original deposition. 



In the quarry of which the last section is given we are introduced 

 to a uew point of interest, which to some extent continues to 

 attract attention, in the openings between this and Oxford, namely 

 a fossiliferous or Natica-hed in the Lower Calcareous Grit. 



In passing north from Marcham, we find that the beds which have 

 just occupied so much of our attention disappear, and the Coral 

 Rag rests directly, as at Westbrook, on the Grit. The exposures in 

 this range are few, and mostly show the sands and girts at the 

 base with their characteristic Ammonites perarmatus, presenting no 

 special points of interest ; but at Bradley farm and at the cross 

 road to Cumnor very instructive sections are seen. 



