GENERAL MEETING. 5 
northwestern California and the adjacent portion of Oregon. This 
island extended as far southeast as the Pit river region where it 
was separated from the main land by a wide strait. 
Ali of the ridges developed out of the Cretacean island belong 
to the Coast range. 
The volcanic ridge of Lassen’s Peak lies between the northern 
end of the Sierra Nevada and the Coast range. The great volcanic 
field of Oregon and Washington Territory, to which Lassen’s Peak 
and the Cascade range belong, appears in a general way to be out- 
lined by the depression between the Cretacean island and the main 
land. A general account of the facts from which these conclusions 
are drawn will appear in Bulletin of the U. S. Geological Sur- 
vey No. 33. 
Mr. I. C. Russewu read a supplementary paper entitled 
NOTES ON THE FAULTS OF THE GREAT BASIN AND OF THE 
EASTERN BASE OF THE SIERRA NEVADA. 
[Abstract. ] 
The structure of the Great Basin was systematically studied by 
the geologists of the Fortieth Parallel Exploration, and subsequently 
by G. K. Gilbert and J. W. Powell. The results of these investiga- 
tions, so far as they relate to the faults of the region, are indicated 
in the bibliographic list which follows. 
The studies here referred to led to the recognition of a type of 
mountain structure named the “Great Basin system,’ which has 
been found to prevail over large portions of the United States west 
of the Rocky Mountains. A typical mountain of this system is a 
long, narrow orographic block, upraised along one edge, 7. e. a mono- 
clinal ridge. A mountain range having this structure usually 
presents an abrupt scarp, formed of the edges of broken strata, 
on ‘the side bordered by the fault, and slopes much more gently 
in the opposite direction. 
Mountain ranges of this character occupy the greater part of the 
area of interior drainage, known as the Great Basin, and at times 
overlap its borders. An older structure in which corrugation plays 
an important part has been recognized by several geologists in the 
desert ranges of Nevada and Utah, but these disturbances were 
produced previous to the faulting which gave origin to the present 
topographic relief. 
