ROCKS AS PLANT-FOOD. 103 



tific comparison. Rocks are bodies saturated with oxygen; 

 and therefore are at rest. 



Plants dijEFer from rocks in a wide degree ; they are com- 

 posed of matter in a state of unrest. They possess a princi- 

 ple which is called vital force, and which leads to constant 

 change until a state of maturity is reached, when, owing to 

 the waning of the vital forces, the antagonistic chemical forces 

 step in and produce decomposition and decay. A plant is 

 under the protection of vital forces during the term of its life, 

 and it has powers of resistance sufficient to keep at bay all 

 oxidizing or chemical agencies, until the time comes when it 

 must l)e resolved back to earth and air from which it came. 

 Rocks by disintegration and chemical change become the food 

 of plants ; that is, the mineral elements are lifted as it were 

 by the aid of vital force into the structure of plants, and they 

 become integral portions of plants. They thus subserve a 

 most important office, — dead, inert, and useless as they seem 

 to be. They encumber our farms, mar the beauty of our 

 tields, break our ploughs and harrows, and cover soils which 

 might be devoted to wheat and corn ; and we scold at their 

 presence, but let us remember that it is from their hated 

 masses that the very pabulum of our cereals is derived, that it 

 is due to them that there is anything to cultivate in our fields. 



The kinds of rocks found in our fields in Massachusetts 

 which belong to the drift period, are, as I have said, not 

 numerous. Granite of different kinds and colors prevails 

 most extensively ; next come quartz, talc, gneiss, and the 

 iron-stones. The latter are found to be quite numerous 

 in the northern counties of the State. In these stones, sul- 

 phide of iron forms a prominent ingredient, and when taken 

 from the ground and exposed to the action of the air, chemi- 

 cal change ensues, and oxide of iron is found upon the 

 surface, giving to the stones a reddish hue. This form of 

 rock is very undesirable for building purposes, and should be 

 ayoided. The stone, when split open, affords to the inex- 

 perienced no special evidence of the presence of iron, and in 

 spite of the care exercised in the construction of my build- 

 ings, several of these stones got in place in the walls, and 

 already are covered with rust. Paint will be needed to pro- 

 tect them from further action. 



