486 ME. E. E. L. DIXON AND DR. A. VATJGHAN ON [Nov. 191 I, 



is uncertain, but the mud appears to have been brecciated 

 in situ by desiccation and cracking, without complete separa- 

 tion into fragments (see p. 514, footnote 6). 



It may be noted that where a calcite-mudstone has succeeded 

 a breccia with uneven upper surface, it has filled up the 

 inequalities and formed a level surface ; in the same way, but 

 on a larger scale, a compact limestone, the lowest bed of a 

 thin Modiola phase, fills up the inequalities in the upper surface 

 of the conglomerate at Pendine (Carmarthenshire), described 

 by Dr. Strahan. 1 



True chert is unknown, but quartz in the peculiar form of 

 minute, colourless and milky-white, zoned nodules of the size 

 of sand-grams, has been noticed in a microscope-slide of one 

 of the laminated limestones. 



The following section illustrates the character of the phase 

 and its relations to the beds above and below : — 



Junction of C and C . — Southern outcrop on the east 

 side of Caswell Bay. 



Thickness in feet. 

 9. Crinoidal limestones, resting sharply on 

 8. Calcite-nmdstone, white-skinned, filling inequalities in 

 7. Breccia : consisting partly of black calcite-mudstone, some 

 of which is fragmentary, and some, though penetrated by 

 the matrix, apparently not completely broken up. The 

 matrix is mudstone and very fine sandstone. With Bed 8. 5 

 6. Thinly-bedded, fine-grained limestones, including oolites. 



With Beds 4 & 5 ... 11 



5. ' Pisolite,' consisting of black, flattened, concentrically- 

 laminated, calcitic 'pisoliths,' up to 0"75 inch in diameter, 

 set in grey finely-crystalline dolomite ; a few inches thick. 

 4. Thinly-bedded to laminated, compact, argillaceous lime- 

 stones. 



3. Dark limestone and black shale, passing into 1^ 



2. Clay-mudstone, with angular or subangular fragments, up 

 to several inches in diameter, of fine-grained, dark oolite 

 such as is found at the top of the Caninia Oolite; 

 lenticular beds of black limestone in the upper part. 



Bests sharply on 1^ 



1. Fine-grained oolite, light or dark grey. 



Total thickness of Modiola phase 18f 



Bed 1 is the top of the Caninia Oolite (CJ ; Beds 2-8 con- 

 stitute the C 2 Modiola phase; and Bed 9 is the base of the 

 standard limestones of C 2 . 



The base of C 2 presents the features described above, which, 

 in conjunction with the faunal peculiarities, show that it con- 

 stitutes a Modiola phase, wherever it has been examined in 

 the eastern district, except in Longland Bay. There it con- 

 sists of a group, a few yards thick, of dark, finely-crystalline 

 dolomites, similar to the Laminosa Dolomites but containing 



1 « The Country around Carmarthen ' Mem. Greol. Surv. 1909, p. 81. 



