400 Proceedings of the Royal Physical Society. 
in the list) wei:e detected in the boulder clay, which came 
from the chalk formation ; these, with the great quantity 
of other chalk material, also in the boulder clay, connected 
with the abundance of chalk flints which are met with all 
over the surface of Caithness, as shown in a paper of mine 
read to the Society some years ago, give room to suspect 
that in all probability the chalk formation, and that pretty 
largely developed, as shown by its widespread ruins, was not 
far distant from Caithness, and it would be well to collect all 
the evidence possible on this desirable and interesting subject. 
The fragmentary state of the organisms proves that they 
could not have lived and died where now found, as no two 
valves were found united (with the exception of two very 
small Anomias) amongst the hundreds of specimens taken 
out of the clay. There is no doubt that these minute shells 
were sheltered in hollows in the rock masses to which they 
were attached when living, and, when these masses w^ere 
removed, held fast by their strong plug, and only became 
loose when this had decayed ; and thus these delicate and 
frail shells escaped destruction. Mr J. Anderson, of Wick, 
got a nice group of young Balani, in a pretty good state of 
preservation, attached to the fragment of a shell. These 
being such rare instances, I have thought it right to men- 
tion them. 
Many of the organisms are microscopic, and were washed 
out of this stubborn clay by myself and Mr J. Anderson, 
and it is thus that the list has been so greatly extended. 
The most abundant shells are Cyprina islandica, Astartes, 
Tellina solidula, Turritella communis ; the latter occur in a 
pretty perfect state, and from microscopic size to more than 
two inches in length, and in such abundance that, in three 
walks up theBurnofHaster,Igot more than eighty specimens, 
and did not take all I saw. However, it would be well not 
to think such great riches are always to be had, for at times 
scarcely any specimens are to be got. A few of the others 
are pretty frequent, whereas Purpura lapillus, Trochus Zizi- 
phinus, Patella vulgata, Mytilus edulis, Mya truncata, Litto- 
rina littorea, Ostrea edulis, and other littoral and shallow- 
