a Theory of the Earth . 195 
cultivated, with its productions, and the kind of culture 
The nature of the basis on which that earth rests. 
3. Rolled pebbles. (See Chap, vih.) 
4. Sand, argil ; their nature ; thickness of their beds. 
5. Nature and thiekness of the strata of the earth at 
the greatest depth possible to be reached, by taking ad 
vantage of the time when wells, mines, and other exca- 
vations are dug. This research is particularly interest- 
ing when these excavations are extended below the level 
of the sea. 
6. Marle-pits ; their external appearances ; whether 
they contain shells, and of what kinds ; extent of their 
beds, and their thickness ; analysis of them, at least with 
acetous acid ; the uses for which the marie is employed. 
7. Clay T pits ; quarries of lime-stoue, gypsum ; mines 
of coal, &c. 
8. Whether the plains exhibit at their surface, or con- 
tain in the interior parts of the earth, vestiges of marine 
bodies, petrified wood, bones, or other substances foreign 
to the soil and to the country. 
9. Internal temperature of the earth, ascertained ei- 
ther by direct experiments, or by observing that of the 
deepest wells or cellars ; or by that of springs, which 
do not freeze in winter, and which remaining cool in 
summer, seem to come from the greatest depths. 
10. Whether any fact can be observed which might 
oblige us to have recourse to the hypothesis of a central 
fire. 
11. Basons surrounded by hills or mountains; whe- 
ther they seem to have been formerly filled with water ; 
whether the water appears to have been fresh or salt ; 
whether any thing indicates the period of its retreat, and 
if there are any traces of the apertures through which it 
escaped. 
