Miscellanies. 381 



A great abundance of hydraulic limestones has been discovered in the 

 Appalachian series, and the interesting fact ascertained or confirmed, 

 that, in all cases, these rocks are highly magnesian. Numerous analyses 

 have settled this point ; well known hydraulic limestones uniformly yield- 

 ing by analysis a large proportion of magnesia, and limestones found by 

 analysis to have a magnesian composition proving on trial to be decidedly 

 hydraulic. When silica is entirely absent the hardening property is di- 

 minished but is still evident, while a small portion of silica is capable of 

 giving full development to the character, provided the magnesia be abun- 

 dant. It has been before proved in one or two instances in England that 

 magnesia produces this effect, but it is now for the first time fully proved 

 in this country by numerous careful analyses attended by corresponding 

 practical trials of the cement. There is reason to conclude that as anal- 

 yses are extended it will prove to be a universal rule that all magnesian 

 limestones are capable of induration under water ; limestones of this 

 description probably form a very large proportion of those of the transi- 

 tion series, particularly in the great valley of Virginia, Pennsylvania, Ma- 

 ryland, and Tennessee ; and the same fact has been abundantly proved 

 as to these limestones from New York and Kentucky. Prof W. B. Rogers 

 finds that in them the carbonate of magnesia is 3 where that of lime is 

 5. The natural bridge of Virginia consists of magnesian limestone a 

 part of which is eminently hydraulic. 



The shells of the tertiary region of Virginia furnish an important 

 resource for agriculture : but the proportion of carbonate of lime in the 

 marls and other earthy mixtures varies very much. Not unfrequently the 

 sulphuric acid formed from pyrites decomposes the carbonate of lime of 

 the shells and forms sulphate of lime, a useful ingredient in the soil ; in 

 which are present also sulphates of iron, alumina, and magnesia, and 

 even free sulphuric acid. The coal of Virginia has in many instances 

 a composition which adapts it happily to use ; the am.ount of bitumen 

 varies between 27 and 38 per cent., the ash from 2 to 5, and the carbon 

 from 75 to 80 ; a composition not unlike that of the Frostburgh coal in 

 Maryland,* combining combustibility, endurance, and intensity. Iron ore 

 is found in vast abundance in Virginia and of an excellent quality : gold 

 is extensively diffused, and although justly regarded as an important in- 

 terest of the State, it is practically of less importance than coal, iron, 

 limestone, and gypsum. There is a large deposit of lead in Wythe 

 county ; and salt springs abound in the valley of the Holston — thirty 

 thousand gallons are evaporated in a day, producing one thousand bushels 

 of salt. 



The sandstones of the Blue Ridge are now known to be subjacent to 

 the limestone of the great valley, and from the peculiar attitude in which 

 this rock, (the sandstone,) is found, and from the marine and littoral 



* Which we have examined in situ and by analysis. 



