concerning the Structure of the Earth. - 259 
44, From this formation of the earth, it will follow, that we 
ought to meet with the same kinds of earths, stones, and mi- 
nerals, appearing at the surface, in long narrow slips, and lying 
parallel to the greatest rise of any long ridges of mountains ; and 
so, in fact, we find them. The Andes in South America, as it 
has been said before, have a chain of volcanos, that extend in 
length above 5000 miles: these volcanos, in all probability, are 
all derived from the same stratum*, Parallel to the Andes, is 
the Sierra, another long ridge of mountains, that run between 
the Andes and the sea; and * these two ridges of mountains run 
within sight of one another, and almost equally, for above a thou- 
sand leagues togetherf,”’ being each, ata medium, about twenty 
leagues wide. The gold and silver mines wrought by the Spa- 
niards, are found in a tract of country parallel to the direction of 
these, and extending through a great part of the length of them. 
45. The same thing is found to obtain in North America also. 
The great lakes, which give rise to the river St. Laurence, are 
kept up by a long ridge of mountains, that run nearly parallel to 
the eastern coast. In descending from these towards the sea‘ 
the same sets of stratat, and in the same order, are generally 
met with throughout the greatest part of their length. 
46. In Great Britain, we have another instance to the same 
purpose, where the direction of the ridge(/) varies about a point 
from due north and south, lying nearly from N. by E. to S. 
by 
which lie parallel to the mountain range, of which alone Mr.M. speaks, but 
others, ranging aimost at right angles to these, in the middle and southern 
and eastern parts of England, Phil. Mag. xxxix. p.271 Note. 
It appears essential; towards the tracing and usefully understanding of 
the subficial structure of any districtof Country, thatall its Strata Ridge and 
Trough Lines, should be surveyed and mapped; I have accomplished a great 
deal of this, with regard to Derbyshire and its environs, to the northern 
parts of Wales (Phil. May. vol. xlv. p. 165), to a considerable portion of 
the south of Scotland, &c., and Mr. Smith alsu has much in store hereon ; 
but while publication remains gratuitous, only to a particular Party, and 
expensive to other labourers in the Geological Field, these labours must 
necessarily be suspended.—J. F. 
* See the notes to art. 36 and 53. See also fig. 3. 
+ See Acosta’s Natural History of the Indies. 
t See Lewis Evans’s Map and Account of North America. 
(h) In adverting so pointedly to a single mountain Ridge, through the 
western side of Great Britain, Mr. Michell is evidently mistaken: the Welch 
mountains of Coarse Slate, &c. present 3 or 4 almost parallel strata Ridges 
and Troughs, of great length, and the same is the case with the middle and 
southern parts of Scotland: the Strata Ridges do not always range through 
the centre of mountain masses—witness the Edinburgh Strata Ridge, which, 
though occasioning the Pentland Hills, docs not pass through them (and 
R2 others 
