1846.] Alluvial Soil of the Mle. 147 



tides of quartz and mica are very abundant, and the magnet takes 

 up a notable portion of magnetic oxide of iron. Particles of 

 highly ferruginous clay are interspersed among it, resembling 

 crumbs of bog iron ore, and leading to the supposition that the 

 heat of the spring is occasioned by the decomposition of pyritous 

 rocks, whose insoluble debris it brings in minute portions to the 

 surface. The gauze sieve already mentioned retains 25 per cent 

 of this sand including nearly all the particles of ferruginous clay. 

 The portion which passes the sieve, resembles, in ahnost every 

 particular, the sandy portion washed out of the newly deposited 

 soil, except of course the different degree of its fineness. Both 

 have particles of red and white quartz, both show magnetic oxide 

 of iron, the sand of the spring in the greater abundance. It is 

 remarked that the particles of this oxide in the portion of sand 

 which passes the sieve, is far greater than in that which remains 

 upon it, which we might anticipate, on the supposition that the 

 sand is brought up by the spring. The greater specific gravity 

 of the paiticles of oxide than that of the quartz, would allow 

 larger masses of the latter than of the former to be thrown up by a 

 current of given velocity. 



Bringing together the results of the analysis of the ancient and 

 that of the most recent soil, we find the following composition in 

 100 parts. 



100.45 

 The loss in the arialysis of the ancient soil, is attributed in part 

 to the combined water, which no doubt existed in the peroxide of 

 iron, and in part to the chloride of sodium and phosphate of alu- 

 mina, of which some traces were observed, but of which time did 

 not allow me to make a minute examination, or to repeat the an- 

 alysis for the purpose of an exact determination of their propor- 

 tion. The most striking difference between the ancient and the 

 modern soils is to be found in the far higher proportion of car- 

 bonic acid, lime, and magnesia in the former, and the greater 



