472 ANALYSES Or GYPSEOUS EARTH. 



silica, alumina, per-oxide of iron, and phosphate of lime were throwiylown, 

 leaving the lime and magnesia alone in a state of suspension. The former 

 was precipitated by oxalate of ammonia, and subsequently the latter by 

 phosphoric acid. 



" The sulphate of lime was ascertained by boiling a determinate quantity 

 of the green-sand in water until the whole of this salt present was taken 

 into solution. The clear solution was treated with chloride of barium, and 

 the sulphate of baryta ignited and weighed. The siilphuric acid present in 

 the earth was thus arrived at, and, by subsequent calculation, the sulphate 

 of lime originally present was ascertained. 



"Sulphate of alumina (but no sulphate of iron) was found to exist, in 

 traces, by the- precipitation of alumina, occasioned on the treatment of 

 the water boiled on the earth with ammonia. But in each case it was too 

 inconsiderable for the determination of its proportion. Chloride of calcium 

 (muriate of lime) was ascertained by treating the same fluid with nitrate 

 of silver. Its proportion did not exceed that in which it exists also in 

 common soils. 



" Results obtained on specimens of green- sand earth from Coggins Point, James 



river. 



" 'No. 1. From 8 inches within the exposed side of a ravine, where a 

 stream flowed by, and 15 feet from the top of the green earth.'* [Mid- 

 dle part of stratum D, see page 465.] 



Hygrometric moisture (lost at 300) . . . 5.50 

 By heating to low redness, it lost in addition 2.03 



Phosphate of lime 0.25 



Carbonate of magnesia, in decided traces. 

 Sulphate of alumina, in traces. 



" 'No. 3. Same as number 1, except from a deeper excavation.' 

 Hygrometric moisture (lost at 300) . . . 4.600 

 By heating to low redness, it lost in addition 2.200 



Carbonate of lime 1.550 



Bi-sulphuret of iron 3.066 



Carbonate of magnesia and sulphate of alumina in traces. 

 Phosphate of lime, about as in number 1. 



Sulphate of lime 0.813 



" 'No. 6. Three feet below the river beach [from pit, lower part of Z>, 

 half a mile distant from preceding.'] 



Hygrometric moisture 5.400 



By heating to low redness, it lost in addition 2.060 



Carbonate of lime 0.535 



Bi-sulphuret of iron 2.060 



Sulphate of lime 0.661 



Carbonate of magnesia and sulphate of alumina in traces. 

 Phosphate of lime as in number 1. 



"'No. 9. See foregoing, page 465. This alone having sulphuret of iron 

 visible in powder, or minute crystals ;' [taken from 14 feet below the 

 beach, in E.~\ 



* This specimen was not thoroughly analyzed, and therefore the contents 

 are reported but in part. The next (No. 3) was deemed the most important, 

 and a more correct specimen of this layer (Z>), and therefore to it the 

 examination of Prof. Shepard was especially requested, and was so directed. 

 It is therefore that the contents of bi-sulphuret of iron, carbonate of lime, 

 and sulphate of lime are not stated of No. 1 , as in No. 3. E. R. 



