272 MESSRS, STRAHAN ANG WALKER ON PEBBLES 
finest-grained green pebbles from the upper part of the conglome- 
rates resemble the sandy beds in the Wenlock shale, but the vast 
majority are totally dissimilar to any rock known in situ in the 
district. On the other hand, they closely resemble the Upper 
Ludlow beds of Kendal and Central Wales, both the red and green 
varieties being referable to these beds*. 
Mr. R. Etheridge has kindly examined some of the pebbles, and 
has named the following genera and species of fossils occurring in 
them :— 
Orthis filosa, Sow., Sil. xx. 21. Wenlock and Ludlow. 
—— lunata, Sow., Sil. xx. 11. Ludlow. 
elegantula, Dalm. Llandeilo to Ludlow. 
cerispa, M‘Coy, Sil. Loss. p. 29. Llandeilo to Ludlow. 
Chonetes striatella=lata, Dalm., Sil. Syst. iti. Ludlow. Four specimens. 
Spirifer crispus, His., Sil. xxi. 4. Llandovery to Ludlow. Five specimens. 
elevatus, Dalm., Sil. xxi. 5,6. Llandovery to Ludlow. 
Rhynckonella Stricklandii, Sow.?, or borealis, Schl. Wenlock. 
: fragments. 
Pterinea retroflexa, Wahl, or lineata, Goldf., Sil. ix. 26. Ludlow. Three 
specimens. 
Orthonotus. 
Arca (or Pterinea ?). 
Theca (?). 
Tentaculites ornatus, Sow., Sil, xxvi. 11, Caradoc to Wenlock. 
Holopella. 
He remarks that they are undoubtedly Upper Silurian and 90 per 
cent. Ludlow, and that the pebbles in their flaggy nature and mica- 
ceous condition resemble beds of this age in Westmoreland. 
In considering from what direction the pebbles have been trans- 
ported it is necessary to bear in mind that, excepting only the 
angular fragments in the Bastard Limestone at the base, not a 
single fragment occurs that is referable to the Wenlock, or any Silu- 
rian rock older than the Wenlock. It is therefore certain that the 
denudation in that area from which the conglomerates were derived 
had not been sufficient to remove the whole of the Ludlow beds and 
expose the underlying Wenlock shales, fragments of which must 
otherwise have occurred in the conglomerates. We must therefore 
look for the source of the pebbles in an area in which the Silurian 
series remained perfect, at least so far as the Lower Ludlow beds, 
when the pre-Carboniferous denudation of these rocks ceased. 
This condition is fulfilled at Ludlow, at a distance of more than 
fifty miles to the south. But over this intervening space the Carbo- 
niferous Limestone is resting on Wenlock shale, which was therefore 
undergoing denudation and contributing débris, Had the drift been 
from this direction, this Wenlock débris must haye been inter- 
mingled. Similarly to the west, near Snowdon and Anglesey, and to the 
north-west, in the Isle of Man, the Carboniferous rest on Wenlock or 
older beds, so that these directions need not be discussed. There 
remains only to be considered the possibility of a source in a north 
or north-easterly direction. 
The removal of the Ludlow beds from the areas of North Wales 
* Qn this point we had the valuable opinion of Mr. W. T. Aveline, F.G.S. 
