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Hints for thé Formation of a Theory of the Earth. 135 
Youred fcoria than when the former varieties exift; a fpeck 
of plumbago is now only found here and there, vind that of 
the fmalleit fize. When the quality of the metal is oxy-, 
genated (No. 4.), not only have the plates of carburet dif- 
appeared, but alfo the coally colour on the external furface of - 
the feoria ; what now attaches to the bars, 1s nearly of the 
fame nature and colour as the lava emitted at-the notch of 
the dam. 
Thefe criterions are ‘fallible; for, 2 as the fufibility or car- 
bonation of the metal is enone in a direét ratio to the 
comparative quantity of the coally principle prefent in the 
furnace, fo in the fame proportion will the vitnid cruft 
encircling the working bars exhibit the prefence of that 
principle in the furnace. 
eee eee SSSSSSSSSSSSSSSSSSSSSSsSSsSSSSsSS9S99n9Snsns9998989nsns9sms er 
1V. Agenda, or a Colle&ion of Obfervations and Refearches 
fe) 3 > 
the Refults of which may ferve as the Foundation for a 
Theory of the Earth, By M. Du Saussure. 
{Continued from Page 29.] 
CH A Pa XSET. 
Errors to be avoided in Ob fer: vations refpeting Geology. 
; ee are fome errors into which people may readily 
fall when they have not had long experience in any given 
kind of obfervation, and againft which it is of importance to 
put beginners at leaft on their guard. . 
2. One may be readily deceived in regard to the relative 
diftances of remote objects. All the ftars and planets appear 
‘to be at an equal diftance from us. Distant mountains all 
appear to be in the fame plain. Thus thofe, which are fitu- 
ated very far behind the reft, feem, to form one body with 
them; fo that people believe they fee continued and uninter- 
rupted chains when there are really none, and) where the 
mountains, on the contrary, are infulated, 
The abfolute diftance of objects, even when not very re- 
mote, is equally difficult to be afcertained on high moun- 
: tains, 
. 
