Correspondence. 295 
thirdly, a bed of clean sand and gravel underlying the clay, and 
containing similar shells and a few boulders, exactly like the top bed. 
This three- fold division is, of course, not invariable; as sometime 
one or two of the members may be absent and the true Boulder-clay, 
_or the Upper Gravel, may rest on the fundamental rock. It is, 
however, well developed in the Severn-valley above Ironbridge, 
where each bed in consecutive superposition attains a thickness of 
60 or 70 feet. The middle bed, or Boulder-clay proper, although 
very various in its composition, does not graduate into either the top 
or bottom gravel, but can be defined to a fewinches. The Shells, 
however, of the whole range, including the underlying gravel, are 
precisely identical ; and their general series indicate a cold climate. 
It would be interesting to know whether the gravelly drift of 
Treland, underlying the Boulder-clay, is merely this bottom-bed of 
gravel or whether its fossil fauna gives evidence of its deposition 
before the Glacial Period; also whether there is any marked 
absence of the glacial striations which have been noticed where the 
Boulder-clay proper rests immediately on a hard fundamental rock. 
I think it will be found that the Moel-Tryfaen gravels, the shells 
of which are still more decidedly Arctic than those of the Severn- 
valley drifts, probably preceded the true Boulder-clay in deposition ; 
as they are covered up with a tough clayey deposit containing 
transported materials, many of which occur as large blocks weighing 
several hundredweights. This top bed is noticed, in the ‘Supple- 
ment’ to ‘The Antiquity of Man,’ as being only 1 foot 9 inches 
thick ; but since the visit made to Moel-Tryfaen by Sir C. Lyell and 
Mr. Symonds in 1868, the operations of the Alexandra Slate Com- 
pany have exposed it to a thickness of from 6 to 15 feet. It has a 
very irregular, though well defined, junction with the underlying 
sand-beds. It contains many more large blocks than the sand, and 
closely resembles in appearance much of the Boulder-clay of the 
Severn-valley. In addition to the species reeorded by Mr. Darbishire 
Mr. GwynJeffreys has determined the following from among a number 
of fragments that I collected from the sand-bed at Moel-'Tryfaen,— 
Tapes virginea, Trophon Barvicense, Cardium fasciatum, and 
Balanus crenatus. 
A few weeks ago I obtained, between Coddenham and Crowfield 
in Suffolk, a number of fragments of shells from the outcrop of a 
bed of clean gravel, which at the latter place is overlain by 60 feet 
of Boulder-clay ; but none of them differed from what occur 
throughout the Glacial Drift of this (Severn-valley) district. 
Whilst on the subject of the Glacial Period, it may be worth 
while recording the existence of an unusually large transported 
block of grey granite in a pond at the back of Hodnet Hall near 
Market-Drayton in this county (Shropshire). It measures 8 feet 
in length, 63 feet in width, and from 6 to 6 feet in thickness ; it is of 
a rounded form and must weigh from 6 to 8 tons. The country in 
the neighbourhood is thickly strewn with blocks of granite and 
greenstone; but none of them at all approach the block at Hod- 
net in size ; indeed it is much larger than any transported block I 
