476 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 20, 



the Old Ked Sandstone. These two formations, when Yon Deehen's 

 Map of the Rhenish Provinces was published, were found to be 

 parallel to the two highest divisions of the Devonian system on the 

 Continent. 



I may now proceed to a few details. 



§ 2. South Pembrokeshire. 



The best section, sheltered from the south-west winds, and acces- 

 sible in part at all tides, is on the eastern side of Caldy Island. The 

 Upper Old Red marls and sandstones, forming the southern horn of 

 Drinkim Bay, end upwards in yellow congiomerates, and are covered 

 by 400 feet of shale and limestone in a most variable series. At the 

 very base are beds of shale with ordinary Carboniferous fossils, such 

 as occur among the alternating shales and calcareous beds beneath 

 the mass (nearly 2000 feet) of the Carboniferous Limestone, and in 

 the base of that rock itself. 



The Old Red Sandstone, therefore, at this locality is abruptly 

 distinct from the overlying beds, in colour, substance, and more 

 especially in its destitution of fossils. 



On the eastern side of the island, where the shales are best seen, 

 I found the upper portion of the Old Red for some distance much 

 softer than the beds below, almost destitute of cornstone, and chiefly 

 consisting of sands and marls of bright colours, mixed with beds of 

 pale conglomerate, which last is persistent through the island, form- 

 ing reefs on either side, and stretching away far into South Pem- 

 brokeshire. This band of pale conglomerates is a good horizon ; by 

 taking advantage of it I was able to compare, bed by bed, the va- 

 riable series of sandstones and marls below ; and on the west side 

 of the island, about 50 feet down in the Old Red series, to my great 

 astonishment, a bed of Serpulce occurred, in masses, like the S.Jllo- 

 grana. I believe the species to be new, and call it Serpula advena 

 (see figure, p. 496). 



Crossing by boat to Skrinkle Bay, of which Be la Beche and 

 Ramsay have given detailed sections, the same beds are visible, even 

 to minute details. It is needless therefore to describe the separate 

 sections. Nearly every bed of calcareous shale, nodular or flat-bedded 

 limestone, cherty sandstone, and oolitic limestone (which is very 

 common) can be traced in the three sections. There is a special 

 group of oolite-beds and grit near the base, a band of oolitic lime- 

 stone two -thirds up, and between the two a remarkable series of 

 thin cherty sandstone -bands, permeated thickly bv the burrows of 

 worms. All of these subgroups are recognizable on the east and west 

 of Caldy Island, at Skrinkle Bay, and, as will be seen afterwards, to 

 the extreme point of Pembrokeshire. 



These sections are all accessible by paths down the cliff, or better 

 still by boat from Tenby. 



At Skrinkle the upper 133 feet of Old Red Sandstone rests on 

 some white sandstones, which are conspicuous at Caldy. The upper 

 37 feet of Old Red is, however, lost by an oblique fault, and this 

 should be borne in mind in comparing the sections. 



