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THE JOURNAL OF GEOLOGY.

Amount of Folding.—Folded structure implies, of course, an alternation of anticlines and synclines. The number of these varies with the intensity of the folding. In the Coast Range there are apparently four or five anticlines and corresponding synclines. In the Sierra they cannot be counted, but there must be very many so closely appressed that the strata seem to be a continuous series dipping all in the same direction, i.e., steeply toward the axis, for at least 30 miles. They cannot form a single series, for this would make an incredible thickness. It must be a series repeated several times by extreme folding; how many, it is impossible now to say. In the Appalachian, according to Claypole[1], there are about 19 anticlines and synclines in 65 miles and in one part—Cumberland valley—there are eight in 16 miles. In the Vaudoise Alps, according to Renevier, there are at least seven[2], and in Savoy as many as 15[3]. In many cases the foldings are so extreme that the strata first rise as folds, then are pushed over beyond the base as overfolds, and finally broken at the crest and upper limb of the fold is pushed over the lower limb many miles horizontally. In the Highlands of Scotland, according to Peach[4], by overthrust, the Archæan is brought over the Silurian and overrides it for ten miles. In the Rocky Mountains of Canada, according to McConnell[5], the Cambrian is brought over the Cretaceous and overrides it for seven miles. In the Appalachian of Georgia, according to Hayes[6], by overthrust, the Cambrian is made to override the Carboniferous for eleven miles.

4. Cleavage Structure.—Closely connected with the last, and having a similar significance, viz., lateral squeezing and mashing, is another structure—cleavage. This structure is often asso-

  1. ↑ Am'n Nat'st, Vol. 19, p. 257 and seq.
  2. ↑ Archives des Science, Vol. 59, p. 5, 1877.
  3. ↑ Archives, Vol. 28, p. 608, 1892, and 25, p. 271, 1893.
  4. ↑ Nature, Vol. 31, p. 29, 1884.
  5. ↑ Geol. Surv. Can. 1886, Rep. D. p. 33.
  6. ↑ Bull. Geol. Soc. Am. Vol. 2, p. 141.
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