214 C. A. White—Jura-Trias of North America. 
divided state as to remain perfectly available to vegetation. 
The double benefit thus gained manifests itself in the exu- 
berant fertility of the soils so treated. I shall hereafter de- 
scribe more in detail the very singular features of the Califor- 
nia alkali soils, but mention the present as a conspicuous ex- 
ample of the benefits to be derived from an intelligent, direct 
investigation of soils. 
Among the many other cases in which the phenomenon of 
flocculation comes into play in technical practice, I only men- 
tion that of ore extraction by means of solvents. Were the 
Art. XX V.—-Remarks on the Jura-Trias of Western North Amer- 
ica; by C. A. Wurre, Paleontologist to the U. S. Geological 
Survey. 
ed as " 
also a certain sandstone formation, usually of a red or reddish 
color, generally present beneath that Jurassic series, has been 
