GEOLOGY. 
41 
Mr. Boyer says: “The-/deposit consists almost entirely of C. mar- 
ginatus and C. robustus of various sizes and often without rims. It 
is impossible, in certain cases, to distinguish between these two 
forms. The variety intermedia is between the two and was created 
by Rattray.” 
The second slide was made from soft shale of the uppermost por¬ 
tion of the Monterey, from the Pinal property on the east side of 
Pine Canyon, on the north flank of Graciosa Ridge. The following 
diatoms were found: 
Coscinodiscus oculus iridis Ehrenberg (abundant) (PI. XI, fig. XIX). 
Coseinodiscus marginatus Ehrenberg. 
Coscinodiscus marginatus var. intermedia Rattray. 
Coscinodiscus robustus Grev. (PI. XX, fig. 4). 
Coscinodiscus radiatus Ehrenberg. 
Coscinodiscus obscurus A. S. (PI. XX, fig. 2). 
Coscinodiscus nodulifer Janisch. 
Coscinodiscus heteroporus Ehrenberg. 
Coscinodiscus subtilis Ehrenberg (PI. XX, fig. 3). 
Actinoptychus undulatus Ehrenberg (rare) (PI. XX, fig. la). 
Arachnodiscus ehrenbergii var. californica (fragment). 
Lithodesmium eornigerum Brun. (PI. XX, fig. 16). 
According to Mr. Boyer this second sample consists chiefly of frag¬ 
ments of Coscinodiscus oculus iridis Ehrenberg, which is a larger and 
more delicate form than the one predominating in the first, and 
both he and Mr. Keeley comment on the peculiar absence of it there. 
The difference in the fauna in these different localities is of interest, 
inasmuch as the deposit represented by the first slide was at the base 
of the Monterey and that represented by the second near its summit. 
Besides the small organisms that have been described as forming 
a portion of the shale material, and the less abundant organic remains 
mentioned on pages 42-43, the deposits of Monterey age contain 
a considerable percentage of fine siliceous and aluminous matter, 
probably of detrital origin, in the shape of exceedingly minute clastic 
grains. The chemical analyses of specimens from different localities 
show a large percentage of alumina, the presence of which is prob¬ 
ably the result of fine argillaceous silt settling on the sea bottom 
to aid in the formation of the shale. The origin of the silica is more 
in doubt. There is no question of the presence of a large amount 
of siliceous diatom skeleton material, and the many fine-rounded and 
angular particles of quartz revealed by the polarizing microscope in 
the unaltered shale indicate that the sediments derived from shore 
areas carried quartz grains also, but there is no proof as to which of 
these sources supplied the bulk of the silica, of which the shale is 
mostly composed. Besides the recognizable diatom remains it is 
impossible to tell how much of the shale is composed of similar skele¬ 
tons that have been crushed beyond any semblance of their original 
form. Comparatively few forms are perfectly preserved, most of 
