Dec, 1845.] 32l 



No. 2. — Specimen of the present soil of the Valley of Korosco, taken at a 

 height of three feet above the Nile. 



This earth is also partly in lumps and partly in powder. Tho former exhibit 

 no marks of stratification, and so far as can be observed, have no tendency to 

 part in one direction more than in another. The texture is open and porous, 

 but the pores are not filled as in No. 1, with any deposite of white matter, ex- 

 cept here and there a rather light gray in the interior of the cavities. In some 

 of the lumps, minute rootlets are seen traversing ihe mass in different directions. 

 The color of this soil is considerably darker than that of No. 1, due in part no 

 doubt to the absence of carbonate of lime. Ferruginous particles abound in 

 this, as in the preceding specimen, but those of mica are of far less frequent 

 occurrence. 



Time has allowed me to make but a few trials to ascertain the composition 

 of this soil, as it was believed to be of more interest to determine the relative 

 characters of the oldest and of the most recent ones, rather than that of an in- 

 termediate period. By twice drying in the inverted syphon apparatus, and in 

 the last instance passing over it 200 cubic inches of air, thoroughly dry, it lost 

 2.6 per cent. By treatment in the apparatus for separating carbonic acid, and 

 boiling five times successively to expel the last atom of that material, using a 

 solution of pure baryta to ascertain when the escaping air, expelled in boiling, 

 ceased to be mixed with that acid, it was found that the amount of carbonic acid 

 was only 1.7 per cent, equivalent to 3.9 per cent, of carbonate of lime. On 

 separating the soil witli the sieve, the finest portion — that passing through the 

 gauze'sieve — was found to afford decidedly more magnetic oxide of iron, than speci- 

 men No. 1. 



No. 3. — Specimen of the earth newly deposited at Korosco, the 18th of 



August, 1844. 



This specimen is entirely in powder, and of a color very nearly approaching 

 that of No. 2. 



Particles of mica are of rather rare occurrence. A few minute fragments of 

 straw or grass are detected, and by a gauze sieve, of which Ihe meshes are 100 

 to the inch, and the spaces to the threads as 2f to 1 in diameter, making the 



open spaces 7 of an inch square only, 22 percent, of this earth was arrested. 



A quantity of very fine fibrous or downy matter was also collected by the seive. 

 Portions of both the coarser and the finer parts of this soil are attracted by the 

 magnet, 4-tentli3 of one per cent, being found in an average portion of it. On 

 being washed, the coarser part is found to be a sand, composed of quartz, red and 

 white, fragments of schorl, and garnets, of magnetic oxide of iron, a little mica, 

 and a few fragments of tubes, such as are seen traversing the older portions of 

 soil already examined. This composition indicates that this specimen has re- 

 sulted from the decomposition ot primitive rocks, and that their debris has been 

 mixed with some portion of the anterior deposits along the river banks. 



Analysis. 



1. Dried 100 grains and found the loss, 3.7 grains. 



2. Transferred the same to a well closed platinum crucible, and ignited ; which 



