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THE JOURNAL OF GEOLOGY.

ous was the time of greatest transgression of sea over the present land areas, while the sea in which the Fusulina beds of Europe and America were formed was more circumscribed.

The Waverly group when traced towards the west gradually takes on the character of deep water formations; it is persistent through Nevada and California,[1] and is known, from unpublished investigations, to have a similar fauna in these two states. The Waverly probably persisted much longer in the west, than in the east, for in northern Missouri C. R. Keyes[2] has observed that in the midst of an undoubted Burlington fauna a well marked Kinderhook or Waverly fauna reappears. This he explained by Barrande's theory of colonies. It is probably an incursion of the inhabitants of a deeper western sea, where the Waverly had persisted longer, into the shallower eastern waters. The work of the Geological Survey of Arkansas shows that a similar phenomenon occurs in that state. The Fayetteville shale, which is probably of Keokuk age, contains a fauna that differs markedly from those of the limestones above and below it. An unpublished report by Professor Henry S. Williams shows the occurrence in the Fayetteville shale of several species that occur in a doubtful upper Devonian or lower Carboniferous black shale in the White Pine district, Nevada. Along with these Devonian or Waverly species occur others that belong much higher, as Productus semireticulatus, and Goniatites conf. sphæricus. Below the Fayetteville shale is the Boone chert, which at the base contains a decided Burlington fauna, and at the top probably belongs to the Keokuk. This has been observed in so many places that there is no possibility of mistake in the sequence of the strata.

We have therefore in Arkansas an incursion similar to that in Missouri, except that in Arkansas the incursion came considerably later. This is evidence that somewhere in the west the Waverly fauna persisted throughout the Burlington, and at least a part of the Keokuk. This is in accordance with the phenomenon described by Professor C. D. Walcott in Monograph VIII.,

  1. ↑ Zoe, Vol. III., p. 274; Proc. Calif. Acad. Sci., Oct. 17, 1892.
  2. ↑ American Journal of Science, December, 1892, p. 447.
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