NOKTH-CAEOLINA GEOLOGICAL SUHVET. 



ble under needful conditions, and it enters largely into the 

 straw of all cereals. 



Alumina never enters into the composition of plants at all ; 

 but it performs an important function notwithstanding; it 

 holds as it were the particles of earth together. Its true of- 

 fice may undoubtedly be shown by experiment. Pour water 

 upon a soil well charged with clay, and it remains upon the 

 surface ; but poured upon sand, it quickly disappears. If 

 the water was charged with fertilizing matter, this also will 

 remain, and be held near the surface by the clay, and within 

 reach of the roots of the plant. 



10. The fact is well known that sandy soils do not retain 

 manures ; while on the contrary, clay soils retain all fertiliz- 

 ing matters with great force. Clay indeed absorbs ammonia 

 under all circumstances, and it cannot be entirely dissipated 

 or driven oif short of a red heat. It obstinately retains water. 

 Some of the functions of clay are performed by other ele- 

 ments. Lime and iron and organic matter, for example, give 

 cohesion to soils, and aid in the retention of water. 



"Water exists in soils in two conditions. In the first, it 

 seems to adhere to the surfaces of particles, and hence is 

 liable to constant variation. This is hygrometric water. In 

 the second, it forms a constituent part of the salts in the soil, 

 as the soluble salts of lime and alkalies, the crenates, etc. In 

 the first instance, it is mostly dissipated by an exposure of 

 400 degrees of Fah., while a heat near to redness is required 

 to remove it from the organic salts. 



All the elements which have been enumerated, except alu- 

 mina, enter into the constitution of plants ; but as I have had 

 occasion to say, in different proportions in different plants, 

 and also in different proportions in the parts of plants. 



An example or two of soils occupying another extreme* 

 where the organic matter is in great excess, may be cited 

 from localities in Tyrrel and Carteret counties. In the for- 

 mer county, large tracts lying upon Croatan Sound, furnish 

 organic matter in great excess, and at the same time they are 

 deficient in the earths. Thus in an uncultivated soil I found 

 it composed of 



