A. L. Leach—Glacial Drift near Amroth. 279 
on the solid rock. It is a very coarse gravel, containing brown and red 
sandstones and red marls (Old Red Sandstone), brown grits and shales, 
yellow grits and quartzites (Coal-measures and Millstone Grit), with 
large well-worn boulders of quartz and pale quartzite. The stones 
are closely packed in a small gravel composed of similar materials. 
The thickness of the gravel is from 4 to 6 feet, its base resting on an 
uneven surface of the stony loam described above. The source of some 
of the rocks is indicated above. All the Old Red Sandstone debris is 
derived from rocks not only outside the basin of the Marros stream 
but separated from it by a deep valley in the Carboniferous Limestone: 
the quartz boulders are also erratics, and an igneous boulder which 
was found in situ in the gravel appears to be derived from some of 
the intrusive igneous rocks of Pembrokeshire, at least 12 or 15 
miles to the north. A considerable proportion of this gravel has 
therefore been derived from beyond the present basin of the stream, 
and some of it has apparently come from the north-western side of 
the broad valley of the Taf. The glacial origin of the gravel is thus 
proved, since no agent except moving ice seems adequate to transport 
material into the Marros Valley over one, if not over two watersheds. 
At its western edge the glacial gravel is overlain by stony loam similar 
to that which underlies the gravel. 
In their formation these drifts belong to two classes; the bottom 
stony loam appears to be a talus of purely local origin accumulated 
against the slopes of the valley during severe climatic conditions and 
subsequently spread out over the floor of the valley. The glacial 
gravel is probably not a true moraine, but water-deposited glacial 
debris formed as an ‘outwash gravel’, the material being derived 
from moraines higher up the valley or on the hills to the north. 
There is no lack of evidence of the glaciation of the district. Glacial 
drifts and numerous erratic boulders occur on these hills and extend 
many miles to the south-west in Pembrokeshire.! On “the ridge 
south-east of Marros” Dr. Strahan? noted a well-glaciated block of 
Millstone Grit. 
The formation of the Marros Valley gravel as an ‘ outwash’ 
deposited by glacial torrents will explain the non-occurrence of 
striated and scratched stones which were vainly sought for in the 
deposit. Any such striations would have been obliterated during the 
formation of the gravel by torrential streams. 
A passing reference was made to the present channel of the stream 
which has cut down through the drifts to the rock, but, in the mouth 
of the valley at least, has not reached the lowest part of the pre- 
glacial floor. Deflected to the east side by the drift, it has cut 
a shallow channel along the rock slope on that side, several feet 
probably above the old stream-course, and now falls to the beach in 
a small cascade. The depth of this new channel, about 3 feet, 
may be taken as an indication of the erosion accomplished by the 
stream mainly in the post-Glacial period. 
1 R. H. Chandler, ‘‘ On some Unrecorded Erratic Boulders in South Pembroke- 
shire’’: Grou. Mac., Dec. V, Vol. VI, No. 589, May, 1909. 
2 Sum. Prog. Geol. Survey, 1908. 
