2'S4: VROY. s. l[. REYNOLDS OX THE LITHOLOGICAL Vol. IxXYli, 



from near the base of D^, liave I foiiiid G-irvaneUa tubules within 

 oolitic gmins : and in this case it is clear that the patches of 

 GirvaneUa acted in the same way as the associated foraminifera, 

 in forming nuclei round which the oolitic grains developed : the 

 tubules do not penetrate the layers of the grains. In a rock a few 

 feet lower down (A 131), it is clear that the grains are composed of 

 Spongiostroiiia material. Lower D, consists, however, in the main, 

 of massive white limestone crowded with foraminifera. Endothyra 

 howmanni is the commonest, but Trocliammina and sometimes 

 y^odosaria and Textuhrria occur. CaJcisplicera is also abundant. 

 There are as well bands of compact limestone of china -stone type 

 (A 13-1) with S2:)ongiosti'oma. 



Very characteristic of D,. thouo*h occurrino- tlirou^'liout D, are 

 bands of the well-marked rock-type ' pseudobreccia.' This was 

 originally described from Gow-er by R. H. Tiddeman, and sub- 

 sequently, more fully, by Mr. E. E. L. Dixon. The rock consists 

 of patches ('fragments') of dark limestone generally crowded with 

 foraminifera surrounded by paler limestone ('matrix"). The 

 limestone of the ' fragments " is partly recrystallized. the change 

 being accompanied by a transference of the contained argillaceous 

 material and iron-oxide to the surrounding 'matrix," which con- 

 sequently tends to be reddish, especially Avhen weathered. These 

 rocks have hitherto, in accounts of the Avon section, been grouped 

 under ' rubbly limestones." It seems, however, that both terms 

 may usefully be retained, though no hard-and-fast line can be 

 drawn between the two rock-types. The term ' rubbly " in the 

 present paper is applied to bands consisting of rounded masses of 

 limestone, often several inches in diameter, embedded in red shaly 

 material. Such bands frequently separate thicker beds of limestone, 

 and probably owe their character to a concretionary or recrystalliza- 

 tion process, whereby the lime gathered in nodules from which the 

 iron and shaly material became separated. The frequently dis- 

 continuous character of the rubbly beds, perhaps depending on 

 local failure of argillaceous material, is shown in PI. IX, tig. i. 



In the railway-cutting four well-marked bands of pseudobreccia 

 are seen in the lower part of D . They are, however, so much 

 weathered, that the conti-ast between 'fragments " and matrix does 

 not clearly show. In the little cutting, however, made for the 

 approach to the platform, north of the tunnel, there is an inter- 

 esting section, including an excellent exposure of unweathered 

 pseudobreccia. 1 The highest band in this little section affords an 

 instance of a ' rubbly " bed. 



Pseudobrecciation, though commonest in foraminiferal limestone, 

 may also occm' in oolites. White, mainly non-oolitic limestones 

 and jDseudobreccias are seen in both the roadside and riverside 

 exposures north of Point Yilla. 



The upper D^ beds seen in the southern half of the railway- 

 cutting behind Point Yilla consist in the main of coarse oolites 



^ The appearance of this rock is identical "nith that illustrated in Q. J. G. S. 

 vol. Ixvii (1911) p]. xxxviii. fig. 2. 



