Suburban Geology of Richmond, Indiana. 307 



I 



always dry. In one of them I found part of the lateral surface 

 covered with an exceedingly light and perfectly pure white sub- 

 stance, to the depth of about an eighth of an inch. Such was 

 its levity and feeble attachment, that a light breath was sufficient 

 to blow it off the rock ; and these characters, united with its 

 whiteness, led me to suppose it was magnesia mechanically sepa- 

 rated from the water trickling into the fissure. I conceive that 

 a constant and forcible current of air, throwing the water into 

 spray, would be adequate to this effect. A process, not very dif- 

 ferent from this, appears to separate the lime from the magnesia 

 in our tea-kettles, causing more of the latter earth to lodge on 

 the higher parts of the vessels : it is in both cases a species of 

 winnowing, the magnesia representing the chaff, and the lime 

 the grain. The substance in question may have been carbonate 

 of lime, (fossil farina,) with no greater proportion of magnesia 

 than the water holds in solution ; but I am inclined to the other 

 opinion ; and I regret that while the fragment of rock covered 

 with the powder was in my possession, the only conclusive evi- 

 * dence of its composition, chemical tests, were not procured. 



North of the town, near the grooved rocks described in the 

 foregoing pages, many tons of calcareous tufa have been formed, 

 involving leaves, stems, twigs, moss, and shells. Some of the 

 impressions of the leaves are beautifully preserved, and are very 

 easily recognized as perfect images of the foliage of beech and 

 sugar-tree. 



la the subterranean vault of a brewer, stalactites are constantly 

 produced; and barrel-heads, staves, and other things, left for 

 some time upon the floor, or standing in unemployed corners of 

 the vault, become coated with carbonate of lime. The stalac- 

 tites are generally tubular and about the size of a large quill : 

 they are removed before they become solid. 



I have suggested above, that the water of this district contains 

 magnesia. By careful evaporation, I find that a gallon of water 

 from ray well contains thirty-two grains and forty-seven hun- 

 dredths of earthy matter, which on analysis proved to be, 



Carbonate of lime, - - 32 grs. 



Carbonate of magnesia, - - 0.47 " 



These are not quite the proportions in which these carbonates 

 exist in our rocks, there being ten hundredths of a grain more 

 ttragnesian carbonate than the same weight of limestone would 



