e DET ۳ مگ‎ A ی‎ THE 
TERTIARY AND MODERN STRATA OF THE BASIN. 183 
do not serve to identify the strata with known formations. These fossils are not only interesting 
and important as the only evidence (aside from lithological characters) of the modern origin of 
the strata, but have peculiarities of structure of great interest to the botanist and student of 
fossil vegetation. Similar fossils were obtained from a silicious boulder on the banks of Posuncula 
River, on the other side of the Sierra Nevada; on comparison, they appear to be identical in 
structure, although differing so much in color and appearance as to leave no doubt of the 
existence of two localities. 
In the Great Basin the stems form beds, with a combined thickness of several feet, lying 
interstratified conformably with the strata on each side. "The beds are almost wholly composed 
of the stems ; they are closely matted together and twisted in various directions. Their color 
is a light bluish-gray, and they are completely silicified so as to preserve every cell and fibre 
with perfect distinctness. The specimens from Posuncula River, being rather larger and less 
compressed, were selected for examination, and slices across the stem were ground down thin 
and polished by the lapidary. These were submitted to Professor Bailey for his examination, 
and he prepared an elaborate figure showing the structure.! It was oco plnied by the follow- 1 
ing explanation : 
“The plants, as far as I can make out the structure, are annual shoots of an exogenous struc- 
ture, presenting a distinct pith, (p. in the drawings); medullary rays (r); a layer of liber (l); 
and a loose succulent bark (b), having large lacunæ (la). ‘In the outer portion of the wood a 
series of large vessels, v 1; of smaller, v 2; and of still smaller ones, v 3, are placed. Icould 
not detect upon these vessels any indications of spiral or dot. 
“The specimens from the east slope of the Sierra agree in all essential points with the above, 
the only difference noticed being the "mn of a few large vessels surrounded with woody 
fibre within the pithy portion. 
**I cannot venture with the limited data furnished above to form any opinion upon the affinities 
of these plants. 
“The vertical section, fig. 1, is made up from observations of-various splinters from different 
parts of the plants which I encased in Canada balsam. The horizontal section, fig. 2, is from 
| the section made by the lapidary in New York, which I afterwards rubbed down to half the 
1 thickness the lapidary had given. The section thus obtained was as perfect as if from a recent 
1 plant. It showed the cells filled with transparent silica, and in the larger lacune the arrange- 
3 ment of the silica into small spherical agates was distinctly visible.” 
The lithological characters of these strata are given in detail in the Itinerary, Chapter V. 
They consist, for the most part, of coarse-grained sandstone and conglomerate, and are upheaved 
at an angle of fifty-four or fifty-five degrees, and trend northeast and southwest. An intrusive 
rock is found in the vicinity. Outcrops of uplifted sandstone also occur as far as the summit of 
the Cañada de las Uvas, which, however, is but little elevated above the general surface of the 
In. As these outcrops occupy the re-entering angle between the end of the Sierra Nevada 
and the Bernardino mountains, they are within the limits of the Basin. The outcrops near the 
summit may be near the source of the Eocene fossils found at the entrance of the pass on the 
western slope. We are thus led to suspect that they are of the age of the Eocene. 
About twenty miles east of the outcrop containing the stems, and near to the entrance of the 
Pass of San Francisquito, there is another interesting exposure of upraised strata, but they are 
Very different in their lithological characters. A great part of theformation is of fine materials; 
1 See Appendix, Article V. 
