. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 334 REPORT OF NATIONAL MUSEUM, 1904. below to show the general character of the work and the now seeming crudity of the ; STRATIFICATION. 35. the strata appear to rest against the sides of the mountain masses; d being the moun- tain, and a a, b b, c c, similar strata of rocks. d \\\\ There is another instance in . which the strata may not ter- minate at their outcrop, but appear again in the opposite hill, as a a, but b b
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 334 REPORT OF NATIONAL MUSEUM, 1904. below to show the general character of the work and the now seeming crudity of the ; STRATIFICATION. 35. the strata appear to rest against the sides of the mountain masses; d being the moun- tain, and a a, b b, c c, similar strata of rocks. d \\\\ There is another instance in . which the strata may not ter- minate at their outcrop, but appear again in the opposite hill, as a a, but b b, by its prolongation, would pass over the hill C. Where the strata are nearly hori- zontal similar strata are almost al ways found on the oppositer sides of 6 a valley, as if they had been formerly con- tinuous, and the valley since formed by some powerful cause. There is another point in relation to stratification, (and it is also applicable to veins, in rocks that are not stratifi- ed,) that, (rom its practical importance in mining, should be well understood. The bed of coal, or vein of ore, ap- pears suddenly to termin- ate. When this occurs, the bed may be found again, either above or below its o- riginal level. At its appa- rent termination, a fissure, or else a different kind of rock, occurs, generally in the form of a vein, as c c. Re- peated observation has shown, that if. at the apparent termination, the rock cutting it off inclines towards you, so as to project over your head, the bed of coal, or other mineral, lies at a lower level on the other side of c c, as though the mass of strata on one side of the vein had slid down to a lower level. In the figure, a a and b b repre- Does the same stratum ever appear on the opposite sides of vallies ? When beds of coal terminate sudden- ly, can they be regained ? and how ? What has been observed of ihe positions of the beds of coal, in refer- ence to the sloping of the vein or dyke? Fig. 27.—Page from Mather's Elements of G
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