1815.) . of Dunblane and Pitcaithly. 363 
be drawn, and which is inconsistent, therefore, with the conclusions 
which in many eases we are able actually to form. We are led, 
therefore, to the admission, that the state of binary combinations 
exist; and it is only necessary to guard against the error of sup- 
ing that the products of the analysis are always the original in 
gredients. f ; 
The importance of the subject, and its relation to the question 
how far chemical analysis is capable of accounting for the medicinal 
efficacy of mineral waters, will, 1 hope, afford an apology for the 
introduction of some of the preceding observations, though they 
may not fall strictly under the objects usually submitted to the~ 
Society. 
—= 
In a succeeding paper I shall have to offer some remarks on the 
analysis of sea-water and salt-brines, suggested by the view which 
I have explained in this: and the same view may perhaps lead to 
the illustration of a geological problem, hitherto involved in consi- 
derable dithculty, the origin of rock salt, and the relation of this 
mineral to the saline impregnation of the ocean. 
ArgticLe IV. 
Geological Qlservations on North Wales. By 1, C. Prichard, 
M.D. F.L.S. F.W.S. &c. 
(To Dr. Thomson.) 
SIR, 
In traversing North Wales during the present summer, I ob- 
served some facts which induce me to suspect that the transition 
formation prevails more extensively in that country than is com- 
monly supposed. ‘The time which I had it in my power to spend 
there being very limited, I had no opportunity of resolving some 
interesting questions which presented themselves to me; but as the 
solution of them would establish an inference important with re- 
spect to the geology of our island, and as they might be easily de- 
termined by any person who could examine at leisure a district of 
no great extent, I venture to suggest them, and to offer my remarks 
to the public through the medium of your Journal, 
_ The greater part of North Wales is occupied by clay-slate, which 
has. all the characteristics of primitive clay-slate, Nearly the whole of 
the tract through which this rock extendsimay be surveyed in clear 
weather from the tops of the three principal mountains of Wales, 
viz. Plinlimmon, Cader Idris, and Snowdon, and a-general idea of 
‘the geological structure of the country may be thus: obtained. It 
consists chiefly of ranges of mountains, which run. from E. to W,, or 
from N,E, to'S.W, ‘These mountains. are generally more abrupt 
