35& The American Geologist. June, 190''. 
the same or about the same age. Broad areas of the Paleozoic 
rocks of the same region are without recognizable fossils. It 
is significant, however, that plant remains do occur in the 
Bragdon formation and that plant remains characterize the 
Mariposa. 
In short, as the meager paleobotanical evidence is without 
weight and besides does not negative a reference of its con- 
tained strata to the Mariposa epoch, and as the structural rela- 
tions of the Bragdon series immistakably point to the late 
Jurassic and also as the Bragdon and Mariposa formations 
are remarkably alike lithologically, yet decidedly different from 
any other formation in California, I consider it natural and 
scientific to refer them both to the same period of time. Of 
course, I recognize that a confident conclusion as to the age of 
the Bragdon will depend on the finding in it of better fossils ; 
but it is not necessary to stand by with folded hands and wait 
for their discovery. 
THE LATE JURASSIC REVOLUTION. 
In some publication of the Geological Society of Ainerica, a 
Bulletin I think, some geologist has suggested that the Cal- 
averas sediments were laid down in a sea extending farther east 
than the present Sierra Nevada region and that then there was 
a physical revolution which raised the sea bottom on the east 
and shifted the shore-line westward so that during the Mar- 
iposa epoch it traversed what is now the middle western slope 
of the Sierra Nevada range. I am writing this paper in the 
mountains where there are no libraries and so cannot give the 
reference, and have even forgotten the name of the person mak- 
ing the suggestion. But it made a strong impression on me 
because in line with a conclusion I had come to with reference 
to the Bragdon formation. In April, 190 r. I suggested* that 
sedimentation ceased in the region west of the Sacramento 
river at the close of the Paleozoic era. but continued in the 
region east of that stream through Triassic and Jurassic time 
up till near the close of the latter, but was then resumed west 
of the Sacramento river. I will amplify this idea. 
Throughout the Klamath region sedimentation ceased at 
the close of the Carboniferous (or the Permian) period. After 
a period of erosion, vulcanism began and the Clear Creek 
• ^MRR. Oeol., vol -xxvii, .\ijril, 1901, p. 23S. 
