1863.] SALTER UPPER OLD RED SANDSTONE. 477 



The shale-series is remarkable for the quantity of broken and 

 rolled Fish-remains. Psammodus or Helodus, Cladodus, and, more 

 rarely, Orodus seem to be the chief cartilaginous Fish, with scales of 

 Palceoniscus in plenty. Black rounded masses, which I cannot but 

 regard as coprolitic, but in which my friend Mr. B,. Smith can find 

 no phosphates, contain bones of Fish, with Shells of Orthoceras, Nu- 

 cula, Cytheropsis, &c. Sometimes rounded masses of this kind seem 

 to have no organisms included in them. All are blackened. Again, 

 rounded masses of the ordinary colour of the shale occur, enclosing 

 Cytheropsis in myriads. Perhaps the whole may be water-worn, as 

 Sir Henry De la Beche suggested* in the case of the very similar 

 Bristol bone -beds. I do not know how to explain the blackening 

 of the included Shells on that view of the case. 



The number and size of the Worm-burrows, often 3 inches broad and 

 many feet in length, form, perhaps, one of the most striking features 

 in the Lower Limestone-shales. They are present, of small size but 

 in great numbers, in the group of cherty rocks before mentioned, and 

 which can be traced, about 70 or 80 feet from the base, throughout 

 the whole of South Pembrokeshire. The action of the "Worms bring- 

 ing clayey matter into sandy beds, and vice versa, gives great tough- 

 ness to the rocks, and they resist the sea- action well. 



Twenty miles to the westward the small bay of West Angle opens 

 at the mouth of Milford Haven, and here a sharp faulted synclinal, 

 in the middle of the bay, permits the whole section to be twice seen 

 in the promontories and reefs on either side of the bay. The sec- 

 tion has changed considerably from what is exhibited on the eastern 

 coast, and nearly 150 feetf more shales are added to the upper part. 

 In these shales a very perfect cleavage is established, fully justifying 

 the term " Carboniferous slate" applied to this formation in Ireland 

 by Sir R. Griffith*. 



Sundry other changes are observable when this section is com- 

 pared with that on the opposite sea-border. The Fish-beds are indeed 

 present, the bands of oolite and grit agree remarkably in the lower 

 part of the section, but the thick bands of limestone are replaced by 

 nodular beds, which indicate a deficiency in the supply of lime. 

 Again, there is a difference of importance near the base, inasmuch 

 as the nodular limestone-bands there contain a vast quantity of a 

 peculiar Bivalve, for which, as I cannot find a name, I have proposed 

 the term Curtonotus (see Appendix, p. 494). It occurs in red lime- 

 stone and grit, to the exclusion of all other fossils, in the bottom 

 bands on the south side of the bay. 



The yellow conglomerates have disappeared, but yellow and brown 

 sandstone has taken their place ; and there is a further remarkable 

 change in the upper part of the Old Bed Sandstone, to which I will 

 direct particular attention. 



* Mem. G-eol, Surv. vol. i. p. 124. 



t The upper part of the Skrinkle section measures 135 feet, that of Angle 

 322 feet. The conditions under which the beds were deposited were greatly 

 different. 



X It is, however, the Lower Limestone-shale of Dr. Smith, as seen at Bristol 

 and the Mendips. 



