jD r. Beddoes’s Obfervations on the 
time, and the injuries of the atmofphere, have removed; 
though I by no means deny that a volcano may force its way 
through pre-exifting rocks of granite. 
There is ftill another analogy between bafaltes and granite, 
more important to the theory of the earth, and lefs liable to 
coil trove rfy than either of the preceding. In their Jituation, 
with refpett to other rocks , we may obferve the fame law . The 
general rule of iuper-pofition, reckoning from below upwards, 
is, i. granite; 2. fchiftus ; 3. limeftone. This rule has 
been found to hold good by fo many mineralogical travellers 
that, though it may not be absolutely univerfal, it muft be 
allowed to prevail very extenfively. Now, in this ifland there 
are numerous inftances where balaltes is Substituted in the feries 
InStead of granite, and where it feems to alternate with gra- 
nite as the fubftratum of other rocks. O11 the road from 
Dolgelly in Merioneth (hire, by Mallwhyd and Cann’s Office, 
through Llanfair to Welchpool, fchiftus appears always in- 
cumbent on whinftone, except fometimes when the latter is 
interjefted between the ftrata, or fqueezed up through fiflures. 
In Wales the country is fo hilly, that the limeftone, if it 
exifted, has probably been waftied away ; but on the confines 
of England it comes in. The road from Welchpool to 
Shrewfbury pafies over the fide of the Long Mountain, which 
confifts of fchiftus ; on the left, or towards the eaft, rife fome 
confiderable bafaitic hills. The ftrata of the Long Mountain 
point towards the fummit of thefe hills, as if the narrow 
valley that intervenes had been cut by water upon the lifted 
edge of the fchiftus. At a fmall diftance from the north and 
fbuth fides of the bafaitic hills calcareous ftiata are found. 
Beyond Shrewsbury, on the road to London, we have, inftead 
of the continued ridges of Wales, a number of infulated, and 
generally 
