Vol. 68.] C.IRBO^IFEROUS LIMESTONE AT UPPER VOBSTER. 65 



(c) Brecciated bands, consisting of rounded and subangiilar fragments 

 of compact horny limestone set in a foraminiferal and shelly limestone- 

 matrix. The fragments are of all sizes up to an inch in diameter. Here 

 and there these brecciated beds contain thin lenticular bands of horny 

 limestone, identical in chai'acter with the fragments; and the prevalent 

 brecciated character of the beds doubtless resulted from the penecontem- 

 poraneous brecciation of such layers. Brecciated beds occur only at the 

 western end of the section. 



In addition, some beds are mottled, and show a well-marked ' con- 

 cretionary ' structure. 



Towards the middle of the northern face, nodular black chert 

 ■occurs in a few beds of compact limestone. 



To the east of this, the predominant rock-type is a brownish- 

 grey limestone, which proves under the microscope to be richly 

 foraminiferal and almost completely recrystallized. 



In the eastern face itself, much of the limestone is oolitic, and 

 some bands of pure oolite occur. Here the beds have suffered 

 local dolomitizatiou. Calcite-veining is very extensive, and the 

 dolomitization appears to be connected with the lines of maximum 

 calcification. One specimen of dolomitic rock, examined in thin 

 section, was found to be an oolitic and foraminiferal limestone in 

 which not only is the matrix almost completely dolomitized, but 

 m.ost of the eoliths also have been attacked. 



Palaeontology. — Altogether, the lithological development is 

 fairly typical of the major upper portion of the Seminula Zone in 

 the Mendips. In the comparative scarcity of fossils, however, this 

 section appears to present a distinctly abnormal development. 

 Occasional bands crowded with Semiimla JicoidesYduWghan ot Litlio- 

 ^trotion martini Ed. & H., can be found, but such beds are far less 

 conspicuous than is usually the case. The other fossils recorded 

 in this section include papilionaceous Chonetes, Athyris cf. 

 sxpansa (Phill.) Dav., Productus aff. cora d'Orb., and Alveolites 

 septosus (Plem.) : among these, only the two former shells are 

 occasionally common. Seminida Jicoides is more abundant in the 

 compact limestones at the western end of the quarry than in 

 the overlying beds on the east. 



With reference to this scarcity of fossils, however, the absence 

 of weathered rock-surfaces throughout most of the quarry should 

 be noted. The detection of fossils is difficult on freshly-broken 

 surfaces of the dark-grey limestones which here predominate. 



The occurrence of Ser20ida in a specimen of limestone obtained from the 

 So beds near the western end of the quarry is a fact worthy of special 

 mention. The calcareous annelid-tubes occur sparingly in a mottled 

 * concretionary ' limestone of compact^ horny texture. I have recently 

 found SoyulcB to be extremely abundant in certain compact, horny lime- 

 rstones of calcite-mudstone ^ type which are intercalated with the Modiola- 

 phase deposits of the Clelstopora Zone in the Mitcheldean district 

 (Grloucestershire). The same fossils might be expected to occur in the 

 shallow-water beds of similar character, so well developed in S2 of the 

 South-Western Province. At the latter horizon, however, they appear to 

 be very rare ; but, in addition to this s|>ecimen from Yobster, I have 

 recently collected a single specimen of compact limestone, crowded with 

 Scrpida, from the Sg beds of the Avon Section. 



^ E. E. L. Dixon, Q. J. a. S. vol. Ixvii (1911) p. 516^ 

 ' Q. J. G. S. IsTo. 269. p 



