a8 Hints for the Formation, of 
a fione with the nitrous.acid, or to Jet fall a.drop of the acid 
(on its furface,. finee the abforbing earth, whateyer it is, may 
Ae only difleminated between, argillaceous or filiceons partie 
cles,» We, mutt, therefore: immerfe),a fragment. of the, fione 
in, a quantity of the acid fuficient todidiolge. it entirely, fi it 
he wholly foluble, and, eblerve wheter there saesiid any — 
Fefiduum that withflands folution, fg ty 7 vtite tiv 
11. Fhe action of the air andiof, meteors often, ne foflils 
appearances abfolutely diferent from thofe which ‘they shad 
_ before they were fubjected torit.,, Wemutt not then be fatif-- 
fied with a fuperficial examination; .¢ mult, found the rocks 
to the quick where the ngsion of meteoric aap has Not per’ 
netrated. - f 
12. People are et seer aoa pare paeneonnd 
ftones as fimple {tones, when the compofition of them, does nat 
manifelt itfelf on the firkt ¥ iew, either on account of the {mall- 
peut of their compofing parts, or becaufe fome of thefe parts ~ 
are cach inclofed feparately in.a eoyering which conceals,the 
interior of them. One may guard;againft this error by.ob- 
Fomving the foil in the fun with ftrong magnifying glaffes, — 
after having moiftened ats furface with water or the, nitrous 
acid, and fill better by expoling it oxadually to the flame of 
the blow-pipe. A + 4 
13. People are often. deceived an regard, to ery Aallifation, 
either im the true form.of the oryfials, or, above all, in.taking ~ 
for real. cryftals\parafite cryitals, or fuch as have hace formed 
in the moulds made\by eryfials of another kind. . Thus,we - 
dee \cryftals of quartz,’ petro-filex, and jafper, formed, in the 
morvlis made by caleareous, eryfials, and which have, affumed 3 
the form of the latter. ul aries 
14, In. régard to, errors, o¢cafioned by ignorance jof the 
ditingive éharasters of foflils, and.of, the:names proper for 
them, the only means of avoiding fuch, errors is toftudy with - 
care goad authors 3 aud, above all, collections formed, or at” 
leaft atrangediand. titled, by,ablemineralogifts. . a 
15. But when ethe, Aightet dowbt,is entertained in “regard 
to the denomination which ought, tobe give en to any fofiil, 
_an exact defeription muf he made either of its external cha- 
raéters or its moti ftriking phyfical properties, fuch as weight 
‘ i Q and 
