Editorial Com went. 325 
associated with the spheroidal basalt, being contemporaneous 
formations. 
5. There are internal features ascribed to the spheroidal 
basalt which are apparently incompatible with the supposi- 
tion that it was a surface flow of lava, (a) The spheroids are 
conspicuously porphyritic (p. 82) and the spaces between 
them are not, but are occupied by a secondary layer of im- 
pure calcite (p. 79) and chlorite. Had these forms been pro- 
duced after eruption as a lava stream there would have been 
porphyritic crystals as frequent in the material filling the 
interstices as in the spheroids, (b) There is a zonal arrange- 
ment apparent in the spheroids (p. 82), and this indicates for 
each an individual, isolated history. This zonal arrangement 
began to be formed before the consolidation of the mass, 
since it caused a zonal distribution of the amygdaloidal struc- 
ture, (c) Each spheroid seems therefore to have been inde- 
pendently under influences which not alone would produce 
amygdaloidal structure, but which operated on the surface of 
each in such a way as to distribute the amygdaloidal cavities 
most numerously about the periphery. When one considers 
the layering of igneous rocks due to successive eruption, and 
the succession of amygdaloidal beds between non-amygdaloi- 
dal and the fortuitous scattering of amygdules over the ex- 
posed surfaces of smaller lava layers, it is apparent that this 
zonal arrangement of amygdaloidal structure may have been 
formed by the contemporaneous exposure of each spheroid 
throughout its entire surface to a common cooling action. It 
seems very questionable whether such exposure could have 
been experienced when they were embraced in a common lava 
stream having a thickness perhaps of fifty to a hundred feet. 
6. The general structural relations will allow the following 
successive steps in this history if the fault plane, which is 
assumed by the author rather than demonstrated, be dis- 
carded. (1) Deposition of the San Francisco sandstone, lower 
portion. (2) Eruption from a volcanic vent in the near vicin- 
ity, forming volcanic bombs, pyroclastic matter and finally 
molten lava streams. (3) The effect of this eruption was to 
substitute locally volcanic and chemical strata for strata 
formed by erosion. This area and this epoch of eruption may 
have been extensive. (4) Subsidence of the area affected be- 
