Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 509 



Confining our attention at present to the first feature, it is 

 concluded that a muddy matrix has undergone partial recrystal- 

 lization, as it were into irregular clots, and thus, by differentiation, 

 quite possibly from a homogeneous state, given rise both to the 

 4 fragments ' — the recrystallized parts, and the ' ground-mass ' — the 

 less crystalline residue. This local recrystallization is inferred, for 

 several reasons, to have taken place shortly after the deposition of 

 the mud. Its peculiar patchiness, in which it differs strongly from 

 late recrystallizations, and its widespread occurrence on the same 

 horizon (D) 1 are most readily explicable on this view. Probably 

 the best reason, however, is that, in Gower, as we shall see, many 

 pseudobreccias have been dolomitized after recrystallization — but 

 while still within the influence of the Avonian sea 2 ; such a view 

 postulates an early age for the recrystallization. The latter, there- 

 fore, appears to be analogous to the early recrystallization known 

 to affect recent calcareous muds, 3 but why it assumed a patchy 

 character is unknown. 



The other features of the pseudobreccias would result directly 

 from a patchy and early recrystallization of a calcareous mud. 

 Recrystallization implies deposition of calcite, and would probably 

 be accompanied by segregation of that mineral and, in a still soft 

 matrix, extrusion of impurity into the unrecrystallized parts. This 

 action would account for the excess of argillaceous matter in the 

 ' ground-mass.' Furthermore, delicate calcareous bodies like 

 foraminifera would tend to disappear from the unrecrystallized 

 parts, to balance, by their dissolution, the deposition of calcite in 

 the recrystallizing areas. 



But, whatever be the ultimate nature of the ' fragments/ their 

 more coarsely crystalline structure in comparison with the ' ground- 

 mass ' has given rise to secondary features of much interest. 

 They appear darker in hand-specimens, on account of their greater 

 translucency. Again, — and this is of far more importance, — they 

 offer a greater resistance to chemical change than the ' ground- 

 mass,' in accordance with the general rule that in calcific rocks 

 such resistance is proportional, cceteris paribus, to the coarse- 

 ness of the crystalline structure. The difference is shown in a 

 variety of ways. The 'fragments,' which may be almost invisible 

 on a fresh surface, often project boldly on weathered faces. 

 Occasionally, it is found that the ' ground-mass ' has recrystallized 

 at some late date completely to coarse calcite-mosaic, but the 

 ' fragments ' included in this mosaic are still unaltered. The 

 difference, however, between the two kinds of material is shown 

 most conspicuously by the difference in their susceptibility to 



1 Pseudobreccias are frequent in D, not only in Gower but also in many 

 other areas both -within and without the South-Western Province. 



2 This view as to the age of the doloinitization is based not only on the 

 original evidence cited in the Swansea Memoir, p. 14, but also on various facts 

 which have come to light since. 



3 See, for instance. E. W. Skeats, Bull. Mus. Comp. Zool. (Harvard) vol. xlii 

 (1903) pp. 105-18, figs. 2 & 4-6. 



2x2 



