BULLETIN OF THE BUSSEY INSTITUTION. 161 
placed upon a natural filter, it is plain that during all the earlier 
stages of the process of disintegration a much larger proportion of the 
finer particles of rock and of the matters derived from the decay of 
mosses and other plants must have been washed away mechanically 
by rain from soils overlying the drift than would usually be removed 
in this way from soils that were in process of formation through the 
decomposition of rocks in place. 
In a subsequent report, it is my intention to discuss more fully the 
potassic manures that are obtainable hereabouts, with the view of 
determining which of them will probably be found most available for 
the New England farmer. 
It has been suggested already that, on account of the liability of 
the soil of different divisions of a large experimental field to vary 
more or less in composition and character, it is neither safe nor easy 
to compare very closely results that have been obtained from plots 
not actually contiguous. But, on the other hand, it is important that 
the results of a considerable number of the experiments should be 
contrasted with one another, in the same way that those from each 
division of the field have been compared, in order that the rela- 
Nore. — Several kinds of rocks, found in place at localities in this vicinity, that 
have already been examined in the Bussey laboratory, contain but little potash, as 
will appear from the following list. I have not as yet been able to procure samples 
of rocks from localities to the northward, whence the drift-gravel of the Plain-field 
came. Contained 
A specimen of soft clay shale, from Morton Street, Jamaica Plain, reteah TIO 
near juuction with Walnut Street . : : : 1.10 
A specimen of soft clay shale, from Everett, on ads of Chelsea, 
near corner of Chelsea Street and Everett Avenue. . pete Aig Sg) 
Rhomboidal clay slate, from quarry near old Powder-House, Elm 
Street, Somerville. : : : aby is : 1.29 
A compact dark-colored rock ovaplendie slate?), from Morton 
Street, as above. Mean of two trials . : a 1.07 
A compact, fine-grained gray rock (trap?), from ‘ red-gravel local- 
ity ” on Clyde Street, Brookline . : : ‘ : ; . 1.00 
“Trap,” from Chelsea Street, Everett, as above . , 0.68 
Syenite, from Rockport, Cape Anna; piece taken from fe Post- 
Office building in Boston . A ’ é : . ; 1.78 
A specimen of very fine-grained granite from a quarry in Ae 
N. H., at the base of Mt. Monadnock . . ‘ 2 ‘ 2 3.66 
Wor, £. 21 
