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FOSSIL PLANTS AS AN AID TO GEOLOGY.
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three species of plants characteristic of the lower Cretaceous, and appears to find its closest resemblance in the older portion of the lower Potomac. Professor Fontaine's results are summed up as follows: "The Glen Rose or alternating strata, in which the fossil plants are found, contain an abundant marine fauna, from the evidence of which Professor Hill had concluded that its age was Neocomian or basal Cretaceous. No fossil plants had hitherto been found in the Comanche series, and the evidence of its age was derived wholly from the animal remains. The discovery of plants in it was, then, of special importance, for it enabled us to compare the evidence of the plant-life with that of the animal life. It is interesting to find so close an agreement. This agreement adds one more proof of the value of fossil floras in fixing the age of the strata in which they are found."

The age of the strata exposed at Gay Head, on the western end of Martha's Vineyard, has been the subject of discussion and speculation by geologists for nearly or quite a hundred years, and the question has only recently been settled. In general the strata have been correlated with the similarly appearing strata of Alum Bay in the Isle of Wight, the position of which is fixed as middle Eocene. It is true that certain Cretaceous shells had been found, but they were not in place, and so intermingled with recent forms, that it was concluded that the age could hardly be other than lower or middle Tertiary. As late as 1889 Professor N. S. Shaler[1] decided, upon purely stratigraphic grounds, that "this part of the Tertiary series is certainly of later Miocene or Pliocene age.

In 1890 Mr. David White visited Martha's Vineyard, and was fortunate enough to find and collect a considerable series of fossil plants from the strata in question. The results of this study[2] showed beyond all doubt that they were of Cretaceous age, many being identical with the plants of the Amboy clays of New Jersey. "The Gay Head flora," Mr. White concludes, "indi-

  1. ↑ Seventh Annual Report U. S. Geol. Survey, 1885-6, p. 332.
  2. ↑ Cf. Am. Jour. Sci., Vol. XXXIX., 1890, pp. 93-101.
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