SOCIETY OF CENTRAL ILLINOIS. 219 



Prof. Burrill — I have about come to the conclusion that on 

 land that does not throw out the plants badly, it is better to leave 

 the mulch off. 



By request, Miss Jennie Brown, of Galva, entertained the Soci- 

 ety, for a short time, with an interesting and well rendered recita- 

 tion, "Kentucky Belle." 



THE GEOLOGY OF SOILS. 

 BY PROF. C. W. ROLFE, CHAMPAIGN". 



The time allotted to this paper will make it necessary to exclude 

 all matters pertaining to artificial fertilization, to the admixture of 

 humus, or to the mechanical condition of the soil, and to limit what 

 is said strictly to its origin and inherent sources of fertility. 



By causing seeds to germinate in pure water, and then adding 

 known quantities of various mineral substances, vegetable physiolo- 

 gists have shown that, while many mineral matters which the plant 

 takes up are of no particular value, others are as essential to its 

 growth, as water or sunlight; that these minerals are such as are not 

 brought to the soil by outside agencies, but are liberated within it, 

 by chemical changes among its constituents, and that the plant can 

 make no use of them until they are brought to it in solution. 



With these facts before us, I am sure no excuse will be thought 

 necessary for bringing before a body of agriculturists some thoughts 

 upon the origin and properties of soils, or the rocks whose decompo- 

 sition produce them. 



Soils are broken down rocks, and hence any inherent resources 

 of fertility the soils may possess must have existed in, and been de- 

 rived from the rocks which formed them. For this reason our study 

 should begin with the origin of the rocks themselves. Let me ask 

 you, then, to go back with me to the time when there was no soil. The 

 earth, existing once as a great drop of molten matter, has contracted, 

 under the influence of its molecular forces until solidification, begin- 

 ning at the center, has reached the surface. The continents are out- 

 lined as elevated plateaus, and the ocean basins as broad lowlands, 

 but no drop of water had fallen, and, of course, no life had been 

 created. The entire surface of the earth was one black and 

 dreary waste of hard, dry, barren, rock, everywhere nearly the same 

 in color and composition. 



This geologists, or better geophysicist believe is a true picture of 

 the earth at that time. 



What was this primitive rock which covered the whole earth and 

 furnished the material for all other kinds? A few facts from chem- 

 ical geology will help me to answer the question. 



If a quantity of pure white sand is mixed with an equal weight 

 of carbonate of soda, and gradually heated, we will see that, before 



