NATURE 



121 



THURSDAY, DECEMBER 12, 1907. 



.l.V UPPER CRETACEOUS FLORA. 



The Cretaceous Flora oj Southern New York and 

 .Vfii' England. By Arthur Hollick. Pp. 219, 

 including 40 plates. (Washington : Government 

 Printing Office, 1906.) 



THE Cretaceous flora is of extreme interest to 

 botanists, for it was during this period that 

 the great, and, as it appears, sudden, change took 

 place from the ancient type of Mesozoic vegetation, 

 with its predominant Cycadophyta and Conifers, to 

 a flora of an essentially modern fades, with the 

 .Vngiosperms already supreme. The recent remark- 

 able work of Dr. Wieland (Nature, vol. Ixxv. , p. 329; 

 vol. l.\.xvi., p. 113) has intensified the interest of this 

 transformation from the old into the new, by show- 

 ing that the Cycadophyta of the earlier Mesozoic had 

 themselves evolved a floral organisation comparable 

 to that ot an Angiosperm, indicating that the 

 dominant groups of the two floras, different as they 

 appear, may yet prove to have been genetically re- 

 lated. 



Dr. Hollick 's monograph relates entirely to an 

 Upper Cretaceous flora in which Angiosperms, or 

 at least Dicotyledons, have completely assumed the 

 •leading rdle, and little trace of their cycad-like pre- 

 decessors remains. The beds yielding the fossil 

 plants belong to the " Island Series " of Dr. Lester 

 Ward, who thus described their distribution : — 



" From Morgan (New Jersey), ... the formation 

 may be traced northward across Staten Island and the 

 northern shore of Long Island, and it re-appears on 

 Martha's Vinevard in the celebrated clifls of Gav 

 Head " (p. 13). 



The horizon of llie beds is mainly that of 

 oLir Upper Chalk (Senonian), and possibly as 

 old, in some cases, as late Cenomanian, but it is 

 doubtful whether the intermediate Turonian is repre- 

 sented (p. 119). An interesting feature of the de- 

 posits is that the concretions containing the plant- 

 remains almost always occur in glacial moraine, or 

 in Cretaceous beds more or less disturbed by glacial 

 action, and scarcelv ever in their original positions 

 (p. 26). 



Of the 222 species to which a systematic position is 

 assigned, six are referred to the Pteridophyta, 27 to 

 the Gymnosperms, four to the Monocotyledons, and 

 no less than 185 to the Dicotyledons. In spite of the 

 many elements of doubt involved in all determinations 

 of more or less fragmentary impressions, these figures 

 piobably give a fair though rough idea of the true 

 proportions, and though further investigation may 

 -omewhat add to the relative importance of the 

 (iymnosperms, there can be no doubt that the 

 Dicotyledons had already completely gained the upper 

 hand in the short interval, geologically speaking, 

 -^incr. Lower Cretaceous times. The Cycadales, the 

 1 h.ir,^ teristic plants of the earlier period, are repre- 

 -nted by a few doubtful fragments. The fossils re- 

 ferred to \MUiamsonia by the author are, as he says, 

 of uncertain affinity, and it has been suggested that 

 they may rather be attributed to Tklagnoliaceae, an 

 M) 1989, \()L. yj] 



order which, on leaf-evidence, was largely represented 

 in the flora. 



The insignificance of the Monocotyledons is another 

 striking point — the four fossils referred to them all 

 seem somewhat dubious. The geological evidence, 

 here and elsewhere, certainly weighs heavily on the 

 side of the opinion, now widely held, that the Dico- 

 tyledons constitute the original angiospermous stock, 

 from which the Monocotyledons have diverged. 



The author's determinations are, at the present 

 stage of investigation, necessarily based almost wholly 

 on impressions of leaves, for such remains of flowers 

 and fruits as have been found seldom seem to have 

 helped materially in the identification. The botanist 

 can rarely feel confidence in conclusions as to affinity 

 derived from leaf-characters alone, and it is to be re- 

 gretted that so many of the fossils are referred to 

 recent genera, the evidence for such attribution being 

 scarcely ever adequate. The author's object has 

 apparently been to identify his specimens, generically 

 or specifically, with those described by previous 

 palaeobotanists, rather than to determine their 

 botanical affinities for himself. As an ample record 

 of a rich flora the monograph has great value, 

 especially from a stratigraphical point of view ; but, 

 as is usually the case with work on LIpper Cretaceous 

 or Tertiary plants, the data will need a far more 

 critical treatment before any accurate botanical con- 

 clusions can be drawn. 



In speaking of the coniferous remains, the author 

 directs attention to the wide and interesting field open 

 for future investigation in the examination of the 

 internal structure of certain specimens. That the 

 structure should so often be preserved is a most hope- 

 ful circumstance, and the work already done on 

 some of this invaluable material by Prof. Jeffrey, of 

 Harvard, partly in conjunction with the present 

 author, shows how much may be looked for when the 

 internal, as w-ell as the superficial, characters of these 

 interesting relics have been more widely investigated. 



D. H. S. 



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