17 
where the smooth surface was broken by the projecting upward of a bed 
of tenacious blue clay that seemed to underlie a large part of the beach for 
it could be seen in several places at a distance from one another. On a 
careful examination I found that this bed of clay was more or less full of 
different organic remains. In one spot I obtained from it abundance of 
specimens of the common mud shell Scrobicularia piperata. They were in 
their natural position hinge upward, and with the two valves united, or 
rather together, the ligament having decayed away. Of this shell 
Woodward says in his Manual of the Mollusca, 4 1 It lives buried in the 
mud of tidal estuaries five or six inches deep." From this fact it seems 
likely that a" change of conditions must have occurred since these molluscs 
were living as the shells were found on the open beach far from the mouth 
of the estuary and where the influence of the land water must be quite 
unfelt. I found none of the same species on the present beach though the 
somewhat similar Mactra stultorum was abundant, and on the other hand 
I did not find a single specimen of Mactra stultorum in the clay. Another 
proof that they are not very recent is afforded by their colour. From 
their long burial in the clay they have acquired the same leaden hue and 
preserve it even after some years exposure to the air. 
While on this part of the subject I may remark that shortly afterwards 
being at Swansea I made careful search along the shores of the Bay for 
any deposit at all resembling what I have above described. After some 
time I found a bed of the same tenacious blue kind of clay and in it were 
abundance of the Sc. piper, as at Bideford Bay in their natural position. 
The principal point of difference was that they occurred only at or near 
the top of the clay, whereas in Devon they were often completely buried in 
it. The part embedded was as before stained of the same colour though 
less permanently, and after a short exposure to the air regained its natural 
whiteness. Here however I found nothing besides. The clay seemed to 
underlie the beach as in North Devon and there was the same distinction 
between the shells in the one and those in the other. 
Not far from the spot first described I found another patch of clay full 
of roots and rootlets which penetrated it in all directions making it appear to 
have been the ground on which vegetation must have grown at some past 
era. Not an inch of it was free from them but I saw no trace of stems or 
leaves. Among these roots was also a large number of spiral univalves 
which therefore may most likely be considered land shells. In form however 
they resemble Rissoa. I have not been able to determine the species with 
certainty. In order to make a fair comparison I searched the neigh- 
