132 Geology of Indiana, §e. 
rains, make a sudden exit through perpendicular perforations 
in the upper stratum of the rock. There are many such cavi- 
ties, which do not receive any water from the surface. Some 
of them are many yards in diameter, forming a regular circular 
concave, of considerable depth, towards the centre. They are 
vulgarly known among the inhabitants by the name of “ sink- 
holes.” ‘The localities of slate are few, and present nothing 
uncommon. =< : 
With regard . to the particular minerals. On Sand Creek, 
60 miles from White River, is an interesting locality of that 
variety of silex, commonly called burrstone. It has been 
examined by several practical millers, who do not hesitate to 
pronounce the specimens which it affords, equal, if not superior, 
to the French burrs. ‘The locality is twenty acres in extent, 
and appears to be. inexhaustible. The mineral varies very 
much in its appearance; it is generally porous, and appears 
to have been puffed up by the escape of some gas, while it 
was in a state of fusion. A mass of well-raised bread gives n0 
inadequate idea of its configuration. It produces most vivid 
sparks with steel. Some labourers are employed in procuring 
millstones from this place; and, such is the size of the sili- 
ceous rocks, that they are under no necessity of constructing 
them of detached masses. They form, of a single rock, mill- 
stones of five and a half feet in diameter, which are not de 
faced by any irregularity, or even earthy cavity. These mill- 
stones may be carried down the White, Wabash, Ohio, and 
‘Mississippi rivers, to New-Orleans, with great facility. And 
if they should prove as excellent as it is expected they i 
this discovery will shed new lustre upon the accumulating evi- 
dence of the mineralogical resources of this republic. 
Many other varieties of silex are common: rock erystal, 
agate, and chalcedony, are often found in the beds of rivulets- 
T passed a considerable distance upon the banks of a small 
stream, called Leather-wood creek: the bottom of the creek Wa 
covered, the whole distance, with siliceous masses, shaped like 
oblate spheroids, and of every size, from that of a large melon 
downwards. On being broken, they presented beautiful geodes 
of crystallized quartz, amethyst, &c. The outside was ofte® 
pp cence PB ge 
