ILLINOIS STATE DAIRYMEN’S ASSOCIATION. 
77 
infiltrations ; which belong respectively to the geological 
periods of their formations, and are soils of great fertility 
and productiveness where there is sufficient rainfall during 
the summer and fall months. 
2nd. The formation of alluvial soils. These soils are 
01 med and deposited in river valleys by the annual over¬ 
low of livers, by the removal of diluvial soils already 
formed and the decomposition of rocks on the mountains 
and hillsides of the river sources drifting their debris or 
sediment, intermixed with vegetable matter, and depositing 
them in their valleys and in deltas at the mouths of rivers 
where they discharge their waters into oceans, bays, seas 
and lakes. These soils partake in character of all the geo¬ 
logical foimations from which these soils were formed, and 
aie generally rich in organic matter and mineral infiltra¬ 
tions, and are the most fertile and self-sustaining of all soils 
mown , as in the valley of the Nile, Ganges, Rhine and 
valleys of rivers in North America. All taken together 
cover large tracts of country. 
3 r d- Soils of volcanic origin. The soils derived from 
volcanic action are of much less extent than either of the 
former ones. They have their origin wholly by the melting 
of the primitive rocks by intense subterranean heat and vol¬ 
canic action. These melted rocks form lava, ashes and 
pumice, which are raised and forced through the craters of 
volcanoes during their eruptions, running down their 
mountain sides into the valleys and plains below them, and 
forming soils partaking of the character of all the rocks 
forming these soils. Volcanoes were more numerous and 
eruptions more frequent in early periods than at present, 
ine sous derived by volcanic action are generally, where 
theie is sufficient rainfall, moderately fertile, as attested by 
the magnificent forests grown on these soils in Oregon 
Washington Territory and British Columbia. S ’ 
The intrinsic value of volcanic action during past ages, 
in contributing means for the advancement of modern civ- 
i ization cannot be fully estimated. By its action mountain 
ranges have been elevated. Their rocks have been tilted, 
bent, twisted and displaced, and their precious metals and 
mineral treasures have been revealed and made accessible 
to the ingenuity of men and used for the purpose of com¬ 
merce and mechanical arts. All this in addition to the for¬ 
mation of valuable soils for agricultural purposes. 
