290 On the Mineralogical Description of Perth. [Marcn, 
that the survey of a district on the north-west of Sheffield,* (where 
it would have been of great importance to have found lime-stone) 
on which I have been engaged, has hitherto prevented my writing. 
“ T have crossed the south-eastern part of the county of Perth, 
and judge, from its appearance, that I should be able to trace every 
individual rock or useful stratum, in all. that district, without any 
difficulty, and lay down its stratification upon a map, which would 
contain much useful and curious information. 
“* The remaining and larger district of the county, to the north- 
west, I am too little acquainted with, from the reports of others, 
to judge of the facility with which the same could be done there, 
or of the value of such a map of the mountain district, when 
made, except as to the situation of its lime-stone rocks. 
“ Neither am I acquainted with the extent, in square miles, of 
the two mineral divisions that might be made of Perthshire, a 
above, or with the state of the best large map of that county. Ifa 
thoroughly good modern map does not already exist, it will be ab- 
solutely necessary, for the purposes of a useful mineral survey, that 
the county map should be revised and filled up, at the time of 
examining and tracing the strata; since the positions of the strata 
are found intimately connected with the streams of water, even to 
the most minute ones, and the abrupt or steeper parts of the surface, 
occasioned by the edges of strata, are alike essential for tracing and 
explaining the internal structure of the district. 
*¢ For preserving and communicating the importantly useful 
knowledge of the stratification and mineral works (as mines, col- 
lieries, quarries, &c.), it is essential that every object on the surface 
should be represented in the map, in order to have a sufficient 
number of known points for exactly describing the situations of the 
several mineral objects. 
‘¢ My want of information on the several points above men- 
tioned makes it impossible for me to attempt any thing like an esti- 
mate of the expense of the proposed survey. 
“ The art of mineral surveying is at present so much in its in- 
fancy that the public in general are not sufficiently acquainted with 
its value to give the same extended encouragement to its professors 
as they do to other arts of longer established importance. On this 
account a surveyor can expect 70 profit from the publication + of 
large mineral maps, but in prudence must look for real employers 
before commencing such works. 
“ The great expense of publishing such surveys as J am in the 
habit of making induces me to take the liberty of suggesting a mode 
of preserving and diffusing the information ; this is, that a Com- 
mittee of a small number of the subscribers should be authorised to 
* See Phil. Mag, xly. 161, since published. 
+ This alludes to a request that the estimate above alluded to might be made 
en the consideration of the mineral surveyor being at liberty to publish the map 
he should make. 
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