444 D. MACKINTOSH ON THE ERRATIC BLOCKS OF 
found two very decided Eskdale-granite pebbles in front of Hasfield 
Court, in fine gravel which had been taken from a low level in the 
neighbourhood. In the streets of Bewdley (and perhaps other 
towns) there are a few good-sized boulders of granite and felstone ; 
but I have been led to believe that they were artificially transported 
from the Bridgenorth neighbourhood at a time when the boating 
traffic on the river Severn was more extensive than at present, 
owing to the introduction of railways*. 
TY. SourH-EAsteRLy EXTENSION OF THE GREAT ARENIG 
FELSTONE-DISPERSION. 
1. Boulder-supplying Capacity of the great Arenig Mountain— 
Initial, Intermediate, and Terminal Concentrations. —As I have 
already described this dispersion in the Quart. Journ. Geol. Soe. 
for December 1874, my present remarks will be almost entirely 
additional. The little and great Arenig mountains, and the escarp- 
ment running south from the latter, furnish a boulder-dispersing 
front about nine miles in lengthy. The great Arenig itself presents 
a precipitous and block-strewn or block-producing front between 
two and three miles in length, and quite 1000 feet above nearly all 
the heights over which the boulders have been transported. The 
radiations of the dispersion include about one fourth of a circle (see I. 
§ 8 and map, Pl. XXII.). Among the initial concentrations the one at 
the east end of Bala lake is the most thickly strewn. A remarkable 
intermediate concentration occurs between Bryn Eglwys and Derwen. 
Terminal concentrations (so far as Wales is concerned) are numerous 
in the neighbourhood of Llangollen; and there is a remarkable one 
around Hryrys, near Llanarmon. I traced these boulders in a north- 
east direction through passes in the Moel Fammau range of hills as 
far as Halkin Mountain, Flintshire—the north-east direction of their 
dispersion from the Arenig corresponding to strize on limestone rocks 
in Grange quarry, near Holywell. The greatest height at which I have 
yet found decided Arenig boulders is about 1900 feet. They are 
generally subangular, often angular, and vary from a very compact 
light bluish-grey felstone to voleanic ashest. Comparatively few of 
the boulders are distinctly brecciated. They are generally very much 
larger and very much less rounded than those derived from the Lake- 
district. The longest I have seen (near Pen-y-bryn, west of Llan- 
gollen) is 17 feet. 
2. Boulders around Chirk and Welsh Frankton.—At the mouth 
of Llangollen vale, about one third of a mile west of Cefn station, 
there is an Arenig boulder 15 x 14 x 10 feet above ground; and about 
* A few small boulders of granite have been found around Birmingham, but 
they may be regarded as mere stragglers from the great granite-dispersions. 
The Rey. J. Caswell found only two small ones in twenty-four square miles 
(British Association Report on Hrratic Blocks for 1877). 
t The Aran Mountains further south may have contributed boulders to the 
Arenig dispersion. 
{ A linear structure is often developed by weathering, and this corroborates 
the general opinion that they are all consolidated volcanic ashes. 
