1890.] PUBLIC DOCUMENT — No. 4. 305 



may also have seen that around the margin of our erratics 

 which project above the surface of the fields, there is com- 

 monly a fertile strip of land in which the crops or the natural 

 vegetation grows more luxuriantly than elsewhere. In good 

 part this fertility of the soil near the bowlder is due to the 

 fact that the decayed matter removed from the surface of the 

 stone is carried by the rain to its margin, and so contributes 

 to the nutrition of plants. 



The extent to which this increase in the fertility of the 

 soil may l)e brought al)out by adding humus to its mass, will 

 depend upon the measure in which the soil seizes upon the 

 mineral substances, and uses them for plant food. In gen- 

 eral, however, it may be said that the glacial soils of New 

 England, even if apparently pure sand of a silicioas nature, 

 contain a sufficient amount of mica, feldspar and other 

 minerals which afford nutritious matter by the action of 

 humus in the mass ; even the thoroughly washed sands of 

 the sea-shore, which appear at first sight purely silicious, 

 really contain a good deal of mineral matter which has a 

 high nutritive value. Generally, however, the proportion 

 of vegetable waste in these sandy soils is very small, and 

 this for the reason that, being readily permeable by water, 

 the vegetable matter is rapidly removed by decay, or leached 

 away by the rains. Experience seems to show that plough- 

 ing in green crops greatly adds to the fertility of these soils, 

 in the first place, by promoting the solution of the mineral 

 matter; and, in the second place, by helping to contain 

 water in seasons of drought. Every bit of decayed vege- 

 table matter acts as a sponge, and yields a certain amount 

 of moisture until it is completely disintegrated by decay. 

 It may be here noted that experience shows that the sea- 

 weeds are particularly valuable in aiding the moisture-retain- 

 ing capacity of the sandy soils ; and this probably for the 

 reason that they have more or less deliquescent salts in their 

 composition, which readily retain moisture until they are 

 dissolved and taken away by the ground water. 



The most considerable difficulty in glacial soils arises from 

 the general absence of a distinct subsoil. Usually these 

 glaciated soils continue with the same character they have 

 near the surface indefinitely downward to a depth far below 



