SECTION FROM THE MISSISSIPPI RIVER TO POUND GAP. 25 
lows, the result of erosion, through the latter of which the 
‘streams of the country flow. The formation is a cavernous 
Saint Louis limestone, the roofs of whose caverns have given 
way in many places and let the surface of the ground fall in, 
forming regular sink-holes, more or less circular in form, often 
‘of the dimensions of wide and deep hollows, but with no out- 
lets. There are no surface streams, and into these sink-holes 
the surface water flows, and the detritus washes and accumu- 
lates. It is natural to expect in such places the most splen- 
did timbers, and such are often found there. 
Again, forest fires have evidently not denuded certain parts 
of the country in the neighborhood of Mammoth Cave. What 
is knownas Doyle’s Valley, for instance, has been, for some rea- 
son, largely protected from the ravages of fire, even if the entire 
district has not been. From the growth of chestnut, I am in- 
clined to think that it has never been continuously burned over. 
On leaving Glasgow Junction, toward Mammoth Cave, plen- 
ty of white oak is found in the sinks; post oak, black oak, 
‘scarlet oak, and red oak are found on the higher grounds, and 
as soon as Chester sandstone, which caps the so-called hills, is 
reached, chestnut is found in great abundance. This is the 
first chestnut worthy of note found, and all that has been 
found, so far, if a few bushes on the silicious limestone, near 
Tennessee river, be excepted; though doubtless all this Ches- 
ter sandstone, from Hopkinsville to Glasgow Junction, would 
have been covered with it, but for the fires that long ago 
swept over this richly timbered country, year after year, and 
‘drove its choicest trees from the forests. 
On the hill sides facing Doyle’s Valley the trees are mag- 
nificent, and white oak, liriodendron, white hickory, massive 
chestnut, scarlet oak, red oak, black oak, Spanish oak, chest- 
nut, ashes, redbud, &c., abound. ’ The chestnut, however, is 
limited to the sandstone, and stops abruptly when the lime- 
‘stone is reached in descending the hill. 
On nearing Mammoth Cave, and all along the banks and 
cliffs of Green river, hornbeam (Carpfinus Americana, often 
‘called iron-wood, but not the true iron-wood) and hop horn- 
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