78 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DoC. 6, 



stones are seen beneath the Monotis-beds, Monotis decussata being 

 characteristic in the West of England of a zone near the top of 

 these beds. 



In the shales here occur the spines and portions of the test of an 

 Echinoderm (Hemipedina ?) : the same species occurs at Stormy. 

 The presence of cubic crystals of Galena in the shales is also note- 

 worthy. This same section may be seen also north of Bridgend, on 

 the Tondu road. 



It will be seen from the foregoing sections how varied are the 

 conditions of the Ehaetic series within a small area. The Pyle 

 valley, enclosed between the two east and west faults mentioned by 

 Sir H. De la Beche *, is much broken by lesser faults ; and to these 

 is, no doubt, due the fragmentary nature of the evidence as to the 

 sequence of the beds. I am unacquainted with any section which 

 shows the position of the Avicula-contorta sandstones in relation to 

 the Sutton and Southerndown series. 



We have seen that some of' the Sutton limestone appears to be 

 below the Monotis-beds, which contain also Axinus elongatus ; they 

 are also below green and purple marls (page 77 swprd). If the green 

 marls in the Stormy cement-works' section be the same as those 

 mentioned near Cwrt-y-Coleman, &c., we have a key to the posi- 

 tion of the Sutton limestones ; they would be below shales containing 

 Avicula contorta. We stiU, however, require the exact relation of 

 the Southerndown to the Avicula-contorta series. 



We have yet to consider the evidence of fossils. And, first, the 

 absence of Avicula contorta from the Sutton series (a shell which is 

 found everywhere, in sandstones, limestones, and shales) would seem 

 to point to more than a mere change in the sea-bottom — namely, to 

 a different horizon in time. Moreover we can scarcely consider the 

 Sutton and Avicula-contorta series contemporaneous, as they are found 

 in close proximity. I believe it probable that the Sutton series was, 

 at any rate, slightly anterior in time to the Avicula-contorta series.. 

 This seems likely from its physical aspect and the abundance in the 

 former of Ostrea multicostata, a characteristic Muschelkalk species, 

 but which has been noticed from the InfraKas of Luxembourg by 

 Terquem ; while, on the other hand, the abundance of Plicatula in- 

 tusstriata, the affinities of the Pectines, Limae, and Cardiniae, show 

 that it must be included in the Rhaetic series. The presence of 

 Ammonites is very remarkable : there seem to be two species pre- 

 sent, at any rate. My specimens, however, are very imperfect. 

 The great paucity, if not entire absence, of Brachiopoda, as com- 

 pared with the foreign beds, is also remarkable. The Sutton beds 

 cannot be regarded as equivalents of the White Lias of the West of 

 England. 



The Southerndown series seems to have been formed under much 

 the same circumstances as that of Sutton, but in deeper water in 

 an area of depression upon the Carboniferous Limestone of this area. 

 The same is the case also with the analogous beds on Broadfield 

 Down, near Bristol, whose similarity of condition was noticed by 

 * Loc. cit. p. 238. 



