SOILS. 15 



pure clay mixed with 5 to 15 per cent, of a silicious sand, 

 which can be separated from it by boiling and decantation. 



3. Clay loam differs from a clay soil, in allowing from 

 15 to 30 per cent, of fine sand to be separated from it by 

 washing, as above described. By this admixture of sand, 

 its parts are mechanically separated, and hence its freer and 

 more friable nature. ^" 



4. A loamy soil deposits from 30 to 60 per cent, of sand, 

 by mechanical washing. 



5. A sandy loam leaves from 60 to 90 per cent', of sand, 

 and 



6. A sandy soil contains no more than ten per cent, of 

 pure clay. 



The mode of examining, with the view of naming soils, 

 as above, is very simple. It is only necessary to spread a 

 weighed quantity of the soil in a thin layer upon writing 

 paper, and to dry it for an hour or two in an oven or upon a 

 hot plate, the heat of which is not sufficient to discolor the 

 paper the loss of weight gives the water it contained. 

 While this is drying, a second weighed portion may be 

 boiled or otherwise thoroughly incorporated with water, and 

 the whole then poured into a vessel, in which the heavy sandy 

 parts are allowed to subside until the fine clay is beginning 

 to settle also. This point must be carefully watched, the 

 liquid then poured off, the sand collected, dried as before 

 upon paper, and again weighed. This weight is the quan- 

 tity of sand in the known weight of moist soil, which by the 

 previous experiment has been found to contain a certain 

 quantity of water. 



Thus, suppose two portions, each 200 grs,, are weighed, 

 and the one in the oven loses 50 grs. of water, and the other 

 leaves 60 grs. of sand, then, the 200 grs. of moist are equal 

 to 150 of dry, and this 150 of dry soil contain 60 of sand, or 

 40 in 100 (40 per cent.). It would, therefore, be properly 

 called a loam, or loamy soil. 



But the above classification has reference only to the clay 

 and sand, while we know that lime is an important constituent 

 of soils, of which they are seldom entirely destitute. We 

 have, therefore, 



7. Marly soils, in which the proportion of lime is more 

 than five but does not exceed 20 per cent, of the whole weight 

 of the dry soil. The marl is a sandy, loamy, or clay marl, 

 according as the proportion of clay it contains would place it 

 under the one or other denomination, supposing it to be 



