410 
OBSERVATIONS ON GEOLOGY, &C. 
Geognosy is understood by him to indicate the distinguish- 
ing, grouping, or classifying, on the great scale, the various 
substances which constitute the exterior parts or crust of 
the globe, that is, all that portion of it of which we ever 
can come to the certain knowledge. For that we should 
pretend to speak of what is at the centre, or in the interior 
of the Earth, is nearly as absurd, I think, as it would be 
(according to the shrewd observation of a worthy gentle- 
man, now no more) to pretend to tell what is in the inside 
of an orange by slightly scratching the rind. The deepest 
mines have certainly not penetrated to any thing like a mile 
into the Earth, and though they had reached thus far, it 
would be only about the four thousandth part of the dis- 
tance from the surface to the centre. But I believe the 
deepest mines have not gone down more than a quarter of 
a mile, or about the sixteen-thousandth part of the earth's 
semidiameter. Therefore we can no more know by all our 
investigations what is at the centre of the earth, than we 
could know what is at Glasgow or Perth (if we had never 
been at either of those places, or had any information con- 
cerning them), by moving four or five yards from the place 
in which we now are. I certainly think it of much conse- 
quence that the object of mineralogical study should be 
rightly understood ; for I have met with not a few who 
seemed to undervalue or avoid it, merely because they had 
formed a wrong notion of the subject ; and, instead of con- 
sidering this science as the means of becoming acquainted 
with the qualities, relations, and uses of the substances of 
the mineral kingdom, looked upon it as nothing more than 
a tissue of vain and unprofitable conjectures about the ori« 
ginal formation of the world. 
