240 Correspondence— Rev. A. Irving. 
Alpine gorges where a stream has had a rapid descent, so that all, or 
nearly all, the sandy materials have been carried away and mutual 
attrition has been the chief agency called into play, the pebble-form 
has been the exception rather than the rule. 
I look upon the variety of the contained fragments of the Bunter 
strata as one of their most important physical characters. This is 
not only true of such great pebble-deposits as the Budleigh Salterton 
Pebble-bed, and those of Sutton Park, near Birmingham ; but it is 
even more marked in the Nottingham type of these beds, in which 
generally the facies presented to us is rather that of a coarse pebbly 
sandstone than. that of a pebble-bed. In these we find very well- 
rolled pebbles of quartz and quartzite ; but we also find fragments 
of such rocks as Millstone-grit, Coal-measure Sandstones, Yoredale 
Sandstones, Magnesian Limestones, along with occasional fragments 
and rolled masses of red Permian Marls, which, with those enumer- 
ated, can be traced to the denudation of the Pennine Highlands. 
These, together with the intercalated (often lenticular) marly bands 
formed in littoral pools, or in channels of contemporaneous erosion, 
are no doubt riverine in their origin ; and, so far as I can recollect, 
are not generally worn into anything like pebbles. This certainly 
cannot be accounted for by their relative hardness. Facts of a similar 
nature in the Severn and Upper Trent country, and in Cheshire, 
have been recorded by Prof. Hull. I regard the strata of the Middle 
Bunter, where rolled detritus chiefly occurs, as a series of shore 
and bay deposits, in which riverine detritus from the ancient land 
is to be found mingled with pebbles (large and small), the latter 
owing their shape mainly to the action of a tidal surf and the 
scouring action of shore-sand. The occurrence of quartzite pebbles 
of Silurian rocks with (occasionally) casts of fossils of the French 
type (as recognized by Salter) in the Salterton pebble-bed (to the 
extent of something like 90 per cent.), the occurrence of similar 
pebbles with (occasionally) casts of Silurian forms in the Warwick- 
shire Bunter, coupled with observations on the work which Mr. Lee 
has actually done upon hard rock-fragments as they are driven along 
shore by the roll of a tidal surf (e.g. between Clovelly and Westward- 
Ho), seem to me to tell rather of shore-action than of river-action as 
the main factor concerned in the production of the Bunter pebbles. 
The “ pebbly sandstone” type of the Middle Bunter is that which 
represents the normal facies, the pebble-beds proper being quite local. 
The two types, however, pass laterally into one another; and the 
main factor concerned in their differentiation was probably the local 
trend of the shore-line in relation to the general direction of the 
tidal flow. Prof. Hull’s memoir, ‘‘The Permian and Triassic Rocks 
of the Midland Counties of England,” is a mine of facts which bear 
out this view. A. Irvine. 
WELLINGTON CotLecE, Berks. 
