Formation in BreclcnoclaMrc. 
S59 
In common routine, the sequel to the history of a trap for- 
mation, should be some attempt to reconcile the appearances I 
have described to one or other of the two prevailing theories ; 
but as I have not the least interest in the inquiry, whether the 
earth was formed by fire or by water, I shall abstain from any 
discussion on the subject. I would merely wish to observe, 
that the hardening of the clay-slate in the neighbourhood of 
the trap, and the intermixture of the two formations, may be as 
well explained, from the way in whicli the consolidation took 
place, as upon the Huttonian notion of subsequent violence. 
I am aware, that the induration of the clay-slate, and the ap- 
pearances of disruption in the adjacency of the trap, will be 
claimed by the Huttonians, as a. fresh verification of their 
theory ; but the impartial geologist will immediately reflect, that 
if the induration of the clay-slate had resulted from the agency 
of fire, the same effect ought always to have taken place ; but I 
have alluded to one spot where the soft clay-slate lies in contact 
with the trap. In fact, from any, thing I saw to the contrary, 
the opposite opinion may be maintained with equal probability, 
—that the trap is the more ancient formation, — that the clay-slate 
had been deposited around it, — and that the disturbance and 
eccentric appearances observable at the foot of the range, were 
the effects of a particular kind of attraction in the crystallizing 
mass naturally ensuing, where one formation ceased, and ano- 
ther began. 
There is one fact which will hardly be looked for, according 
to either theory. In crossing over from Llandrindod to Bettys, 
I found an opening in the very midst of the trap deposit en- 
tirely of clay-slate. 
Art. VIII. — Description of a New Perspective Machine By 
the late James Watt, Esq, LL. D, F. R. S. Lond. and 
Edin. Member of the National Institute of France, and of 
the Batavian Society of Rotterdam, 
The perspective machine w as invented about 1765, in conse^ 
quence of my friend Dr James Lind having brought from In- 
* The Editor is in possession of one of these machines, presented to hini by 
Mr Watt, and constructed by himself. 
