STATE AGRICULTURAL SOCIETY. 187 



lumps; but it is difficult to find any condition of moisture at which 

 it is easily tillable. It is free from all coarse particles, all passing 

 through a sieve having meshes of 1-50 of an inch. The mechanical 

 analysis gave the following result: 



No. 643. — Black Waxy Adobe. 

 Fine earth All. 



Mechanical Analysis of Fine Earth. 



Clay 43.54 



Sediment of ■<0.25 mm. hydraulic value 34.05 



Sediment of 0.25 mm 1.59 



Sediment of 0.5 mm. 2.59 



Sediment of 1.0 mm. 3.13 



Sediment of 2.0 mm 2.79 



Sediment of 4.0 mm. 2.26 



Sediment of 8.0 mm — 1.76 



Sediment of 16.0 mm .75 



Sediment of 32.0 mm 



Sediment of 64.0 mm. ( 



Total 94.68 



Few tillable soils thus far analyzed show a higher clay percentage 

 than this, which is not unlike the " buckshot soil " of the Mississippi 

 bottom, in the proportion of its finest ingredients; but diff'ers in that 

 in the latter there is a gradual, regular "tapering off"" from the finest 

 toward the coarsest, while in the California soil there is one of those 

 sudden breaks in the percentages, which seems in all cases to imply 

 heaviness in tillage. The chemical analysis resulted thus: 



59.98 



No. 643 — Chemical Analysis. 



Insoluble matter 50.96] 



Soluble silica - 9.02 j 



Potash .19 



Soda .74 



Lime 2.47 



Magnesia .89 



Br. oxide of manganese .07 



Pero.xide of iron 11.09 



Alumina 15.69 



Phosphoric acid .06 



Sulpliuric acid .05 



Carbonic acid Trace 



V/ater and organic matter 8.30 



Total 99.52 



Humus 1.50 



Available inorganic .83 



Hygroscopic moisture 13.5 



Absorbed at 13.5° C. 



The remarkably small percentage of potash, and the high one of 

 soda shown in this analysis, led to a repetition of the determination, 

 but with a similar result. The phosphoric acid likewise is in small 

 supply, while the amount of lime (two and one half per cent) is high, 

 and should render the soil susceptible of better tillage than it seems 

 to attain in ordinary practice, especially as the humus supply is quite 

 large. But of all adobe soils thus far examined, this is the poorest 

 in potash and phosphates, and therefore the least durable in cultiva- 

 tion. The black adobe soils of the San Ramon Valley proper, how- 



