316 G. W. LAMPLUGH ON SHELLY PATCHES IN THE 
what scattered, as if through the shearing of the whole mass after 
the shells were broken ; so that they often occurred as a little streak 
of angular fragments in the clay. But even where the crushing 
had been most severe, absolutely uninjured specimens might occa- 
sionally be obtained. For instance, I have myself dug out a single 
specimen of Astarte compressa, with valves united and in perfect 
preservation, from a mass of blue clay of limited area, in which L 
was unable by the closest search to find another unbroken vaive. 
In a similar manner, at Dimlington I found one perfect specimen of 
Tellina balthica in a small pocket of sand no larger than a man’s 
head, in which I could not discover another shell, broken or unbroken. 
And I once found in the Basement Boulder-clay itself, on the South 
Sands at Bridlington, what we may regard as a shell-patch reduced 
to its lowest dimensions, a complete specimen of the same TVellina 
(single valves are not rare), with valves closed and filled in with 
sand, but with no trace of sandy matrix outside the shell. 
Though, personally, I only obtained unbroken a few of the stronger 
bivalves, such as one or two species of Astarte, Mya truncata, Pholas 
crispata, Saxicava rugosa, and other species, the thorough and com- 
plete mode of research adopted by Mr. Headley brought to light 
magnificent examples of such shells as Nucula Cobboldie, Tellinu 
calcaria, and several species of Leda, as well as a very large number 
of the smaller shells, especially univalves, which have escaped injury 
far oftener than the larger individuals. 
The mode of occurrence of Pholas crispata is worthy of special 
remark. This shell is chiefly found in the centre of a blunt cylinder 
of hardened sand, which forms a faithful cast of the lower part of 
its boring. This cast often includes other shells, and is, of course, a 
sample of the sea-bottom on which the mollusk lived. The sand, 
though lighter in colour, has the same general appearance as that 
which is so generally diffused through the clay masses. In similar 
casts which [ obtained from the beds at Dimlington, thirty-two miles 
further south, the matrix closely resembles that of the Bridlington 
specimens, a fact of great importance in considering the origin of 
the deposit. : 
1 think, from the sharp and delicate nature of most of these casts, 
that the boring must have been made in stiff clay. The mollusk 
probably burrowed down from the sandy floor on which it lived into 
beds of the fine biue clay which now forms the chief part of the 
masses, and the ice has ploughed through the sandy sea-bottom 
into these clays, kneading both together and removing them in 
mass. 
Having now stated the chief facts respecting the deposit which 
came under my observation, I will briefly indicate what seems to 
me to be their bearing on the question of its origin. 
That the beds are not in place will, I think, be clear to most. 
But if any still deem the evidence insufficient, I would refer to my 
letter in the ‘ Geological Magazine’ for August 1882, where the case 
is discussed. 
The question arises,—Of what age are the beds; since if they be 
