146 “ate Hints for the Formation of 
tains, where the tranfparency of the air, and the. abfetice of 
vapours, deftroy the aérial perfpective. I have oftem-ima- ; 
gined that I had only two or three hundred fteps to make in 
order to reach a fummit, the diftance of which from me was 
more than a leacue in a firaight line. 
3. There ate a oreat many errors in regard to ftrata. Their 
great thicknefs may make one believe “that there are none — 
where they really exift. In the like manner , if the vertical 
ftrata, or thofe only very much inclined,- prefent their planes” 
to the eye of the obferver, he will think he fees fhapelefs and 
indivifible matics; while, if their feétions were feen, their 
divifions would readily be diftinguithed. A mountain then 
muit be feen under afpects that interfect each other at right 
angles before we can pronounce that it is not divided by 
ftrata. : 
4. At other times accidental fiffures, but produced how- 
ever by a caufe which is common to them, exhibit the ap- 
pearance of ftrata when there are none; or when, if there 
are, their fituation is very different from that of thofe ftrata. 
It is the internal tifue of the flone only which in many cafes 
can determine whether the divifions obferved are the interftices 
between ftrata or mere fiflures; becaufe the ftrata are con- 
ftantly parallel to the internal Jamine, or fchiftous texture of 
the ftone. Cryftals, the Jamellated texture of which may 
fometimes be confounded with a fchiftous texture, may af- 
ford an ex¢eption to this rule, by prefenting lamine perpeh- 
dicular to the planes of the firata; but it is not difficult to 
diftinguith them. - ; 
5. One may alfo form an erroneous opinion refpecting a 
the direGtion of a mountain, or of its ftrata, when the eye is 4 
not fituated in their prolongation, or at leaft near it. 
6. The apparent fituation of the ftrata may alfo lead into 
an error. They appear horizontal even w hen they are very — 
much incliried,‘and when they are not feen but in a fection -— 
formed by a plane parallel to the common fection of their 
planes with the horizon. It is im poffible to judge of their — 
inclination, and to meafure it with certainty, but on’a fee~ 7 
‘tion perpendicular to the common fe¢tion, w hich I have jut t 
‘Miehttoned. 4 
ve 
