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altitude and reaches south into Mexico. This mountain belt 
was once the margin of the Pacific ocean. Its crest is crowned 
by volcanic cones like gigantic towers of a fortification. The 
central portion of this plateau was called by Fremont “ the 
great basin” as it forms a hydrographic basin drained by 
the Columbia and Colorado. The former makes its way to 
the ocean through a gorge in the Cascade Mountains, whilst 
the latter escapes to the south through a series of Cafions, of 
which the most important is nearly a thousand miles in 
length, and from three to six thousand feet deep. In Vol. 
VI. of the Pacific Rail Road Reports the country of the 
Columbia is described and the reasons for concluding that it 
had cut its way through the Cascade Mountains, and similar 
facts were observed in the district drained by the Klamath 
and Pit Rivers. Certain peculiarities are to be seen in the 
country between the Sierra Nevada and Rocky Mountains. 
In the northern and middle portions of the great table lands 
the surface is somewhat thickly set by short and isolated 
mountain ranges, sometimes called “the lost mountains.” 
These rise like islands above the level of the plain, and are 
generally composed of volcanic or metamorphic rocks. The 
spaces between them are level desert surfaces. ‘T'owards the 
north and west, on the tributaries of the Columbia, Klamath 
or Pit Rivers, the plateau is cut by these streams, and the 
deposit can be examined. The rocks are nearly horizontal, 
some are coarse volcanic ash, with fragments of pumice and 
scoriz. Others denominated “concrete” resemble the old 
Roman Cement. Many are quite white and are generally 
‘known as “ chalk-beds” though they contain no lime. The 
late Prof. J. W. Bailey determined these to consist of the 
remains of fresh water species of Diatomaceze. The stratifi- 
cation and horizontality of these beds show them to have 
been thrown down from great bodies of water which once 
covered the greater part of these level plains. 
From south-western Idaho and eastern Oregon, have lately 
been brought large collections of animal and vegetable fossils, 
of great variety and interest. The plants were mostly col- 
lected by Rey. Thomas Congdon, of the Dalles, Oregon, at 
