THE WEST OF ENGLAND AND EAST OF WALES. 427 
at first sight might be mistaken for the granite of a part, at least, of 
Cleopatra’s needle); but on this beach, in different boulders and 
pebbles, it can be seen graduating into the typical Criffel. The 
Arenig rocks zn situ vary from compact felstone to consolidated 
yoleanic ashes; but all the gradations may be found among the 
boulders which, at different heights, have been scattered east and 
north-east. ‘Tracing boulders continuously back to their sources, 
where it can be done, is the most reliable means of identification. 
It may here be remarked that it is better to give a general or geolo- 
gical name to the kind of rock of which a boulder consists than a very 
precise mineralogical name, because many single boulders are large 
enough to embrace more or less variety in their structure and compo- 
sition. The appearance of the weathered surface is often almost 
sufficient to identify a boulder; and the shape and size ought not to 
be left out of consideration. The Arenig-felstone and Criffel-granite 
boulders are often very large, almost invariably angular or sub- 
angular, and seldom glaciated. The Eskdale-granite and Lake- 
district-felstone boulders vary in size ; but they are generally smaller 
than the boulders just mentioned, and in most instances are rounded, 
smoothed, and more or less glaciated*. 
4. Intercrossing of Courses of Boulders.—In mapping the directions 
in which boulders have been dispersed, no fact is more clearly brought 
out than the intercrossing of the courses, not only of local with great 
boulder-dispersions, but of the latter with each other. For instance, 
the Eskdale granite which went to Burton (Shropshire), must have 
crossed the course of the stream of Criffel granite which went to the 
west and north of Wolverhampton, because Eskdale is situated east 
of Criffel; and Burton west of Wolverhampton. It is possible that 
on a small scale this intercrossing of routes may have been effected 
contemporaneously by upper and under boulder-bearing currents ; 
but it is not likely that the above two large dispersions should have 
forced their way across each other without being either broken up 
or commingled to a very much greater extent than is actually the 
case in their terminal concentrations. As we have reason to believe 
(see § 5, 7) that boulder-laden currents would change their courses 
with the rising and falling of the sea-bed, as well as with changes 
of temperature, it seems most likely that the crossing of the courses 
of great boulder-dispersions occurred at different periods. The great 
Arenig stream of boulders would appear to have crossed the previous 
route of the Burton dispersion after the land had become much more 
deeply submerged (see IV. § 3). 
5. Conterminous Gramte and Felstone Dispersions—Effects of local 
Obstructions.—Granite and felstone from the Lake-district and granite 
from Criffel may all three have been transported at different times. 
In that case nothing but persistent (for the required time) local ob- 
structions could have caused their frontal boundaries to coincide ; 
and these obstructions may have consisted of suddenly rising ground, 
* T may here mention that I have nowhere found a greater amount of agree- 
ment in the direction of the longer axes of la:ge boulders than might reasonably 
be referred to chance. 
