THE GLACIAL DEPOSITS OF NORTHERN PEMBROKESHIRE, 67 
18 feet, and is followed above by Sand and Upper Boulder-Clay. The Lower Boulder- 
Clay is partly exposed in the cutting, and is full of fragments of marine shells. 
There is also a small exposure in the moor just south of Letterston. 
That the boulder-clay occurs far inland is proved by an examination of a pit at 
Llyn, near Llangolman, not far from Maenclochog. When seen the pit was only 5 
feet deep, but it is opened up by the farmers periodically to a depth of from 15 to 
20 feet, and ladders have to be used to get in and out. The clay is bluish in colour 
and very tough, and is usually spoken of by the natives as “indiarubber clay.” 
It occurs in boggy land at the bottom of a small valley, at a level of over 400 feet. 
On both sides the land rises to a higher level, and is covered by a mantle of sands and 
gravels. 
West of Goodwick the blue clay comes to the surface just below St Nicholas Church, 
at Clyn Bach moor. The depth was not ascertained. Fragments of broken shells 
occur here, though somewhat rarely. Some boulders of igneous rocks, foreign to the 
district, were found, and among them an unmistakable boulder of the Ailsa Craig 
riebeckite micro-granite. 
The bluish clay is seen at places as far as the western end of the promontory—such 
as in the moors around Trefain, and in the shallow pits at Henllys, below Llanrian, 
where very fine examples of chalk flints were seen included. In the pits of Trefeithan 
moor, west of St David’s, this boulder-clay is exposed to a depth of 6 feet and is of the 
usual character. No shells were seen, but some vegetable matter occurs in the clay. 
The boulders were few, and those noted were all of local rocks. Somewhat similar 
but shallower pits may be seen on Dowrog moor, Tretio moor, and Caer-farchell 
moor. 
It is thus evident that this Lower Boulder-Clay occurs throughout the district, but 
it appears to thicken as we pass from west to east, and to be best developed to the 
east of Strumble Head. Fragments of marine shells were found in the clay at Cardigan, 
at Dinas, at the railway cutting near Tregroes, and at St Nicholas, and for the deter- 
mination of these and other shells mentioned in this paper the writer is indebted to 
Mr Henry Woops, M.A., St John’s College, Cambridge. Owing to their fragmentary 
condition it has been difficult to identify with certainty the shells found in the clay. 
But the following species appear to be represented :— 
CaRDIGAN CLAY-PIT—— 
Pectunculus glycimeris, L. 
Astarte sulcata, Da Costa. 
Mytilus, sp. 
Dinas Ciay-Pir— 
Astarte (Nicania) compressa, Mont. 
(2) Cyprina islandica, L. 
