PART II. ol 
lavas. These soils have a high clay content, but so wonderful is their 
crumb structure that they work like medium loams. Their original 
vegetation was forest but much has been cleared. Most of the coffee 
plantations are on this type of soil. 
The Naivashan lavas in all probability give rise to much of the 
soil of the Trans-Nzoia. Unfortunately little is known of the geology 
of this area, but if Professor Gregory is correct in his estimate of the 
age of Mount Elgon, there can be no doubt but that much of this area 
is derived from this series. Little can be said regarding the soils of 
the Trans-Nzoia. 
During the Pleistocene period the volcanoes of Longonot, Suswa, 
and Menengai, among others, were active. Ash and scorie from them 
covered the soils then in existence. In parts, this is especially marked 
on the upper slopes of Menengai and in the Kedong Valley, the 
particles of ash remain unchanged. Tower down the slopes of 
Menengai the character of the soil changes considerably. The fresh 
scorize disappear, the soil becomes more clayey and possesses a certain 
structure absent from the soil above. These modifications are probably 
due to admixture with the Nyassan series and the action of water 
weathering some of the finer ash particles to a colloidal condition. 
The vegetal relationships on the soils in this area are most interesting. 
The mechanical composition of these soils has been considerably 
influenced by climatic conditions. In the more arid regions the 
original particles are hardly affected and the humus content of the 
soil is low. Where moister conditions have obtained, weathering 
changes have proceeded far with the formation of inorganic colloids, 
besides there has been a tendency for humus to collect. The soils of 
the drier parts are thus liable to pass into the single grain condition 
very readily under cultivation, where similarily derived soils containing 
more humus and fine fractions would retain their crumb structure 
longer. 
There is a general idea that voleanic soils are extremely rich in all 
plant nutrients and that all the farmer has to do is to till the soil and 
plant his seed when wonderful crops will be returned indefinitely. It 
being being known that the soils of the Kenya Highlands are volcanic 
in origin, this idea had a great deal to do with the origin of the 
pernicious system of single crop farming practised, in which the farmer 
has képt his soil under the same crop continuously without the 
addition of any manure whatsoever. If it had been possible, not even 
the bare fallowing, that the climate has necessitated, would have 
been allowed. It has been noticed by some farmers, that the drop in 
crop production cannot be ascribed solely to the African scape-goat— 
decreasing rainfall. There was, they concluded. a lack of plant 
nutrients; manuring has followed. 
The soils of Kenya, in common with the majority of African soils, 
are, on the whole, deficient in phosphates. Although it has not been 
possible, until recently, to conduct any manurial experiments, the use 
of phosphates has been widely recommended. Whereever such 
manuring has been practised good results have followed, but, so far, 
no reliable figures have been available. Nitrogen deficiency has been 
indicated in certain parts and crops have responded to dressings of 
nitrogenous manure. These deficiencies of nutrients are easily 
rectified. The deterioration in physical condition, that the farming 
practices in Kenya have, and are, causing will give more difficulty. 
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