344 PEOF. S. H. REYNOLDS AND DR. A. VATTGHAN ON [Aug. 191 I, 



II. Description of the Important Bock-Types, arranged 



ZONALLY AND LlTHOLOOICALLY. (S. H. R.) 



[The traverse is from north to south, the zones being thus 

 encountered in descending order.] 



VISEAN. 



Lower Dibunophyllum Zone (D x ). 



Extent. — The top of Quarry 1 and the hillside on the north. 

 Thickness. — A thickness of about 20 feet is exposed in the 

 quarry, and perhaps 80 feet beyoud it. 



The D beds exposed consist entirely of fine-grained and crys- 

 talline grey limestone. The red coloration, which is as a rule so 

 characteristic of the D beds of the Bristol district, is not seen at 

 Burrington. The rocks exposed in the quarry are uniformly and 

 somewhat strongly crinoidal. In some bands Dibunophyllum is 

 sufficiently abundant to form an appreciable part of the rock. 

 Sections show that the limestone exposed on the hillside is full of 

 foraminifera, and much like that forming the bulk of the S and C 2 

 beds. 



Upper Seminula Zone (S 2 ). 



Extent. — Erom nearly the top of Quarry 1 to nearly the top of 

 Quarry 2. 



Thickness. — 540 feet. 



The S 2 beds maybe subdivided as follows, in descending order : — 



S 2 (d). Thinly-bedded, very variable series, consisting in the main 

 of compaot horny limestone (china-stone) often concretionary and 

 showing imperfect ' Cotham-Marble ' structure, alternating with 

 limestone often oolitic containing Seminula bands, and including a 

 more shaly development in the upper part. This horizon is the 

 representative of the ' concretionary beds '■ of the Avon, Sodbury, 

 and other sections in the neighbourhood of Bristol, and is exposed 

 in Quarry 1. 



S 2 (c). Eine-grained, generally foraminiferal grey limestone, with 

 Seminula bands. Exposed on the hillside. 



S 2 (6). Eine-grained grey limestone, containing many strong bands 

 of Lithostrotion martini and much chert. Exposed on the hillside. 



S 2 (a). Grey limestone, commonly oolitic ; the upper beds are very 

 poorly exposed on the hillside, the lower are well seen in Quarry 2. 

 A little dolomitization has occurred at one level in the upper beds. 



Eurther Account of the Lithology of the S„ Beds. 



Many of the lithological types occurring in the Burrington section 

 are identical with those of the Avon section, and have been already 



