46S Hints for the Formation of 
really none, and where the mountains, on the contrary, 
are insulated. 
The absolute distance of objects, even when not very 
remote, is equally difficult to be ascertained on high 
mountains, wffiere the transparency of the air, and the 
absence of vapours, destroy the aerial perspective. I 
have often imagined that I had only two or three hun- 
dred steps to make in order to reach a summit, the dis- 
tance of which from me was more than a league in a 
straight line. 
3. There are a great many errors in regard to strata. 
Their great thickness may make one believe that there, 
are none where they really exist. In the like manner, 
if the vertical strata, or those only very much inclined, 
present their planes to the eye of the observer, he will 
think he sees shapeless and indivisible masses ; while, if 
their sections were seen, their divisions would readily be 
distinguished. A mountain then must be seen under 
aspects that intersect each. other at right angles before we 
can pronounce that it is not divided by strata. 
4. At other times accidental fissures, but produced 
however by a cause which is common to them, exhibit 
the appearance of strata when there are none : or when, 
if there are, their situation is very different from that of 
those strata. It is the internal tissue of the stone only 
which in many cases can determine whether the divi- 
sions observed are the interstices between strata or mere 
fissures ; because the strata are constantly parallel to the 
internal laminae, or schistous texture of the stone. Crys- 
tals, the lamellated texture of which may sometimes be 
confounded with a schistous texture, may afford an ex- 
ception to this rule, by presenting laminae perpendicular 
to the planes of the strata ; but it is not difficult to distin- 
guish them. 
5. One may also form an erroneous opinion respecting 
