310 J. F. BLAKE AND W. H. HUDLESTON ON 



be 30 feet altgether. The lower portion is more compact and 

 crystalline than the upper, and contains a bed of Coral Rag in a 

 state of crystallized limestone. 



We have seen rubbly oolites overlying the representative of the 

 Rag near Cumnor ; but the great thickness here of beds of a 

 calcareous nature above the actual coral growth is a very unusual 

 phenomenon. 



Prof. Phillips has noticed the patchy character of the calcareous 

 beds on the surface, and refers it partly to denudation ; but cer- 

 tainly, if wc may judge from their changing character, they were 

 never very continuous. 



The Headington type is continued onto the opposite hills to the 

 north, as may be seen in a quarry on the road to Stanton St. John, 

 the Rag and shelly beds inosculating ; but on crossing a fault, as 

 drawn in the Survey map (quarter-sheet 45, S.E.), and reaching 

 the last-named village, a new type has set in. 



Close to the symbol s^ 40 is a very remarkable quarry. Here 

 about 24 feet are seen, composed of alternate layers of hard dog- 

 gery bands and marl. Towards the base the hard bands are closer 

 together, thicker, and more crystalline, the lowest being a hard 

 blue compact limestone 1 foot in thickness, with fragments of shells. 

 The lower marly beds are more like a small calcareous brash than 

 true marl, which becomes, however, more abundant towards the top. 

 We see here something of the Hillmarton type of Rag ; but the argil- 

 laceous matter is by no means so abundant, nor is it so connected 

 with Coral ; for what is remarkable in the fauna here is, that all 

 corals seem to be absent or very scarce, nor are there any Pectens 

 to be seen. It is, however, a complete nest of Echinoderms, the 

 chief being Cidaris florigemma, Pseudodiadema versipora, Echino- 

 brissus scutatus, and Dysaster (?). The accompanying fossils are 

 Ammonites plicatilis, Chemnitzia heddingtonensis, Gervillia avicu- 

 loides, Lima rigida, L. dlvptica, and Exogyra nana. 



We see here the spot where the corals did not grow, as at 

 Headington we saw where they did. Here we have the debris of 

 the ground-up, variably hardened reef, along with the Echinoderms 

 that lived in the neighbourhood ; and we thus have a natural ter- 

 mination of the Coral Rag in this direction. 



The Cidaris-Jlorigemmabeds are here immediately underlain by thin 

 flaggy calcareous grits, rather ferruginous and full of shells, which 

 are quarried for road-metal. They have much resemblance to beds 

 in a similar position with reference to the Lower Calcareous Grit in 

 Yorkshire, but are a type of rock not much seen in Oxfordshire ; so 

 that even these lower beds vary. 



On the south of Headington a somewhat similar type of rock may 

 be seen overlying the Lower Calcareous Grit in the Littlemore 

 cutting ; but, unfortunately, it appears to be very unfossiliferous. 

 About 14 feet of alternate clays and limestones are here seen, the 

 upper limestones decayed as at Hillmarton, and some of the clays 

 having a considerable thickness. The only fossils noted being 

 Krogyra nana and Astarte, sp. (cf. ovata), we are left in some doubt 



