206 FORMATION OF SURFACE SOIL 



There are other sections, where foreign accumula* 

 ticns cover the original soil, and alter its capabilities, 

 from causes that we can more fully comprehend, 

 causes which are operating at the present day. These 

 are alluvial plains, formed by substances deposited 

 during the annual overflow of rivers. These, during 

 high water, become charged in the rapid currents of 

 their sources, with materials from all of the formations 

 through which their course lies. When the water 

 reaches the plains of the low countries, where it has 

 room to expand beyond its usual limits, a deposit of 

 these suspended substances takes place, as soon as the 

 current is checked by spreading out over the surface, 

 and its flow becomes tranquil. 



Thus an annual layer is formed, which in time 

 makes a soil of great depth, and usually of great fer- 

 tility; for the >eason that it is a mixture from the 

 ruins of many rocks, and therefore likely to contain 

 all that plants need. We have many instances of such 

 soils in this country; on the banks of the Connecticut, 

 of the Mohawk, of the Mississippi, and a hundred other 

 streams. 



These causes, then, are sufficient reasons for saying 

 that we can not always assert what any particular 

 soil will be, if we know the rock of the district in 

 which it is situated. Our opinion upon such a sub- 

 ject must be given with the reservation — " If there 

 have been no disturbing influences." An inspection 

 of a district by a practised eye, would immediately 

 detect any foreign deposits, and determine their cha- 

 racter. 



It is easy to perceive how a knowledge of this sub- 

 ject, even of a superficial nature, must oe valuable 

 to a practical man I*/ his soil is formed by the de- 

 composition of a granitic rock, he can ascertain with 

 little trouble, what are the constituents of that rock, 

 and what are the special manures most likely to 



