132 Geology of Indiana, ^c. 



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, 

 00 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 no 

 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 ca.vity. These mill- 

 stones may be carried down the White, Wabash, Ohio, and 

 Mississippi rivers, to New-Orleans, with great facihty. And 

 if they sl|ould prove as excellent as it is expected they will, 

 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 crystal, 

 agate, and chalcedony, are often found in the beds of rivulets. I 

 passed a considerable distance upon the banks of asmall stream, 

 called Leather-wood creek : the bottom of the creek was co- 

 vered, 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. Tbe outside was ofte^. 



