PLATE 31, FIGURE 2
"Alnus n. sp.?" Hollick, Summary Kept. (loc. cit.), p. 134.
This fragmentary specimen represents a piece of the upper portion of a leaf that is suggestive of the obovate forms of several existing American species of alder, such as Alnus serrulata Willdenow, A. fruticosa Ruprecht, and A. oblongifolia Torrey, and the Old World species A. rotundifolia Miller (=A. glutinosa Miller)—especially the last, which is a common element in the European Pleistocene flora. This was also described by Reid,11 based upon identification of seeds, from deposits regarded as Pliocene in age, and by Marty,12 based upon folial identifications, from deposits regarded as of Miocene age. In particular our specimen may be compared with the similar large fragmentary one represented by Marty's figure 2, plate 3 (op. cit.); and except for its much larger size it is suggestive of specimens from the Pleistocene (Talbot formation) of Maryland, described and figured by the writer13 and referred to the existing eastern North American species Alnus rugosa K. Koch (= A. serrulata Willdenow). Our specimen, in its entirety, was apparently obovate in shape, with a somewhat uneven or wavy margin, finely dentate, the dentitions consisting of an obscurely defined major series with minor denticulations between. Its fragmentary condition renders impossible either a specific description or a positive identification that would be of any value.
Incidentally, it is of interest to note, in connection with the several species above mentioned, that the general type of alder leaf that they represent has an ancestry that began as far back as the Miocene in the Old World, and in America also according to Newberry,14 who described and figured a leaf from the Miocene of Bridge Creek, Oregon, under the name Alnus serrulata fossilis (op. cit., p. 66, pl. 46, fig. 6), and remarked: "Among the leaves . . . occurs one . . . which . . . it will be seen at a glance . . . closely resembles the leaves of A. serrulata, and I have been unable to find any characters upon which to base a distinction. More material will, of course, be needed before the fact may be considered established that our most common alder was growing in the Tertiary. There would be nothing surprising, however, in such a discovery; indeed it was to be expected that this species, so wide-spread as it now is, should have some representative in the Tertiary flora."
From the above references and citations it may be inferred that any fossil alder leaf of the general type represented by those of the several existing species discussed would not be of much value in critical stratigraphic investigations, and any statement that might express or imply definite identification with any existing species might lead to erroneous conclusions in regard to areal as well as vertical distribution. A species of alder ("Alnus sp.") was also listed by Penhallow (loc. cit., 1900, pp. 335 and 338), from the Canadian Pleistocene of the Don Eiver Valley, but without any description or illustration.