Geology, 413 



taking accurate measurements of the distance between the thallium-h"ne 

 and the principal lines of the solar spectrum. 



This green line is an exquisitely delicate test for the presence of thal- 

 lium, and shows it to be a somewhat widely distributed element. Many 

 specimens of crude sulphur contain it (especially when rather dark-look- 

 ing). In most cases it is only necessary to set fire to as large a piece of 

 sulphur (less than a pea) as the platiniura loop will hold, and when it 

 has nearly burned away to blow it out, and then introduce it at leisure 

 into the flame of the spectroscope, for the thallium to show its presence 

 by a bright-green line which will flash for an instant into the field of 



TecHXICAL CHEHtSTRT.— 



11. For Photographic copying in pure Black and White. — In copying 

 maps, printed matter, enacravings, <fec., the following will be found an ex- 

 cellent method. After fixing a delicate negative, wash very carefully. 

 Then flood with a solution of free iodine in iodid of potassium, two 

 grains of the iodid to one grain of the iodine in the ounce of water, 

 l^ilute with water to a sherry pale color, or dark, as may be found neces- 

 sary. Wash well and fix. Repeat the process, if necessary. The in- 

 available. The liquid becomes colorless, by degrees; go on until it is 

 quite colorless. To intensify, use Russell's developer for the tannin pro- 

 cess, until experience shows you have suflScient intensity. Now immerse 

 totally in bichlorid of mercury in acidulated water. One drop of nitric 

 acid to six ounces of water. Wash very thoroughly. Flood with weak 

 iodid of potassium, adding gradually to its strength until the deepest 

 yellow with a tinge of olive color is obtained by transmitted light. 

 Wash again, and treat with chlorid of gold, one gram to the ounce of 



II. GEOLOGY. 

 1. Observations on the Appalachian region of Southern Virginia ;hy 

 J. P. Lesley (from an account of the Coal formation of Southern \ ir- 

 giina, in the Proc. Amer. Phil. Soc, Jan., 1862).— The coal region of 

 Montcromery, Pulaski, Wythe, Washington, and Smith counties in South- 

 ern Virginia, is interesting in an economical as well as a geological sense. 

 It furnishes species of serai anthracite and semi-bituminous coal, which 

 come in competition with the Mesozoic bituminous coal of the Richmond 

 hasin, over the principal internal railroad of the Southern Atlantic States. 

 This railroad penetrates the great primary range of mountains, the Blue 

 Ridge, at Lynchbunr, and then follows the course of the Great \ alley, 

 soutbwestward, to Knoxville and Chattanooga, in Eastern Tennessee. 

 on"thJHudson to Montgomery "n" Alabama, everywhere separating the 

 range of the Bine Rridge, South Mountain, Smoky Mountain, or Black 

 HilK from the true Alleghanies or Appalachians. The rocks of the Blue 

 Ridge range, on the eastern side of the Valley are a prolongation of 

 the Green Mmmtains of Vermont, and consist of the Quebec group or 

 Taconic system, now understood by Logan to be a thickening ot the low- 

 est Silurian (Calciferous Sandrock and Potsdam Sandstone or Primal 



