352 THE BEGOLITH 



any of the above constituents counts for little when they are 

 combined in the form of difficultly soluble silicates. A granitic 

 rock, as has already been noted, contains locked up in its mass 

 all the mineral elements necessary for a fertile soil, but remains 

 barren simply because these are in a condition of slight solu- 

 bility and its physical structure is such that even the soluble 

 portions are unavailable. Pulverize this rock sufficiently, and 

 it will become immediately available for soil, though naturally 

 its fertility is slight, and rendered enduring only by gradual 

 decomposition. It is of course possible, that by nature's methods, 

 decomposition and incident leaching may have gone so far that 

 a soil on the immediate surface, though derived from rocks rich 

 in essential constituents, has become quite impoverished and 

 barren. This is especially true with limestone residuals, as has 

 been already noted. It is doubtless to this fact that is due the 

 enduring qualities of the glacial till as a soil, though its immedi- 

 ate fertility may not be as great as one of sedentary origin. The 

 undecomposed feldspathic and other mineral particles contained 

 by the till, due to its mechanical origin, yield up slowly but 

 continually their supply of plant food, and such a soil may long 

 outlast the residual clays of non-glaciated regions. 



Soils derived from deposits of modified glacial drift are 

 almost invariably sandy or gravelly in their nature. Such, on 

 account of their easy working qualities, great porosity, and 

 ready permeability, are commonly known as light soils, even 

 though their actual specific gravities may be greater than the 

 so-called heavy soils of the ground moraine.^ 



^ Mecliaiiical analysis of a glacial soil from an old pasture, Cape Eliza- 

 beth, Maine, yielded results as below. The portion selected was of just the 

 thickness turned up by the plough,— about 7 inches. In color it was dark 

 gray, at the immediate surface almost black from organic matter, and 

 penetrated throughout by grass roots. Fine angular grains of white quartz 

 were the most conspicuous feature on macroscopic examination. Eight hun- 

 dred and thirty grammes of this soil on sifting yielded: (1) 2.5 grammes 

 gravel, which failed to pass a sieve containing 8 meshes to the lineal inch. 

 This consisted mainly of angular quartz and cleavage bits of feldspar with 

 occasional rounded lumps of impure limonite, and not completely disin- 

 tegrated particles of granitic rock. (2) 40 grammes coarse sand retained 

 by 20-mesh sieve and consisting of clear glassy and white opaque quartz 

 in angular and sub-angular fragments, the largest forms being some 3 

 millimetres in greatest diameter j cleavage bits of white and pink feldspar, 

 rarely folia of white mica, a few bits of mica schist, and lastly hard, 

 rounded pellets of indurated silt and organic matter. (3) 170 grammes 



