678 GEOLOGY OF OHIO. 



which the village of Yellow Springs derives its name will be treated by 

 itself, but all along the gorges in the Niagara limestone voluminous 

 springs are issuing, which are making extensive calcareous deposits, 

 sometimes in dome-shaped stalagmitic masses under the dripping of the 

 springs, but more frequently mingled with the earthy and organic prod- 

 ucts over and among which the waters flow in short slopes to the valley. 

 The vegetable, and sometimes the animal, matters that the water meets 

 with are often incrusted by the travertine, and are then said in popular 

 language to be petrified. A specimen submitted to analyses gave the 

 following result (Wormley) : 



Carbonate of lime 95.70 



Carbonate of magnesia 3.73 



Alumina and iron 0.50 



99.93 



Another specimen examined shows the following composition (Mees): 



Carbonate of lime 97.60 



Carbonate of magnesia 1.21 



Silicious matter 0.60 



99.41 



In this connection the very interesting fact is to be noted, that while 

 the rocks from which the springs issue are dolomitic, containing nearly as 

 much carbonate of magnesia as carbonate of lime, the travertine is almost 

 purely calcareous. It therefore appears that in magnesian limestones 

 permeated by atmospheric waters the proportions of magnesia must be 

 constantly, though of course very slowly, increasing. The varying pro- 

 portions of carbonate of magnesia in the limestones of the Cedarville 

 division may be, in part, accounted for in this way. By reference to the 

 table of analyses on page 675, it will be seen that this substance in one 

 instance makes fifty per cent, of the entire weight of the rock. A greater 

 exposure than ordinary to carbonated waters would serve to explain this 

 increased proportion. It may be added that the location of the quarry 

 from which the stone yielding this result was obtained, in the fiat-lying 

 tract of Darke county, would seem to indicate the long-continued pres- 

 ence of such .carbonated water. 



Further : as far as the explanation above given applies, it ought to be 

 found that the more highly magnesian the limestone the less should be 

 its specific gravity. A few facts under this head are here given. The 

 determinations of specific gravity were furnished by Prof. Mendenhall, of 

 the Ohio Agricultural and Mechanical College. The comparison is not 



