NA TURE 



189 



THURSDAY, JUNE 20, 1S78 



TERTIARY FLORA OF NORTH AMERICA 



United States Geological Survey of the Territories — 

 Tertiary Flora. By L. Lesquereux. VoL vii. 

 (Washington, 1878.) 



THE volume for the present year, of considerable 

 thickness,' is entirely occupied by a most important 

 work upon the Tertiary flora of North America. Although 

 the geological and stratigraphical portions of the work 

 are not so distinctly set out as they might have been, this 

 by no means lessens the palasontological value of the 

 work which is more especially in the author's province. 



The country occupied by the Lignitic beds, described 

 in the present volume, is a plain stretching for 600 miles 

 between the Missouri and the Rocky Mountains. The 

 ascending gradient is not more than ten feet per mile and 

 the beds are horizontal ; the whole Lignitic series is 

 therefore exposed in sequence from east to west, com- 

 mencing with the Cretaceous lignites, described in a 

 previous volume (which occupy about one-third of the 

 area), and ending with the newer Miocene or perhaps 

 Pliocene beds. 



The Tertiary Lignitic coal-fields of Western America 

 alone, were estimated by Taylor in 1848 to occupy the 

 enormous area of 250,000 square miles, or twice the area 

 of Great Britain ; but M. Lesquereux supposes that coal- 

 beds of other ages must be included, and he points out 

 (p. 7) that nothing positive was known of the great North 

 American Lignitic until Dr. Hayden began his researches 

 in 1854, and to the remarkable accuracy of whose work 

 he pays a well-merited tribute. 



Their area on the Upper Missouri is stated at not less 

 than 100,000 square miles, and in the succeeding para- 

 graph it is estimated at about 140,000 miles. This is their 

 extent in that region of the United States alone, but their 

 actual extent is much greater, since they stretch far across 

 the border into British possessions; they have been traced 

 southward along the base of the Laramie range to beyond 

 the Arkansas River, and by outliers as far as Albuquerque, 

 and again westward they are connected with the coal- 

 fields of the Great Colorado Basin and the Laramie 

 Plains. 



Under the heading " Stratigraphy" we are told that there 

 is no unconformability, physical, or other break in the 

 sequence from the so-called Cretaceous lignites to the 

 Tertiary Lignitic. It is then mentioned that there is a 

 transition bed of coarse sandstone, irregularly deposited, 

 whose thickness is not stated. There are next given 

 detailed sections, some of Upper and some of Lower 

 Lignite, none of them, however, presenting a thickness of 

 more than 480 feet. It is strange that only a small para- 

 graph (p. 12), extracted from Hayden' s Report in 1874, 

 to which no prominence is given, warns us that the 

 Lower Lignites are of vast thickness — 3,000 to 5,000 feet, 

 but whether this thickness is all of Tertiary or the older 

 lignites we are left to ascertain elsewhere, whilst we only 

 incidentally gather that there is an Upper and a Lower 

 Lignite. The faulty construction of the introduction 

 arises from M. Lesquereux having too loosely strung 



' About 380 pages and 65 plates. 



Vol. XVIII. — No. 451 



together extracts from various works, which render it so 

 disconnected as to be all but useless except to those who 

 possess a previous knowledge of the subject. The thick- 

 ness of, and as far as possible, the area occupied by, 

 each division of the Lignite should have been as clearly 

 set out as we find them in Hayden' s Report for 1S74, 

 which is frequently referred to in the present work. 



The third section is almost wholly occupied by verbatirrt^ 

 extracts from the arguments of Professors Hayden", 

 Meek, and Cope as to the age of the Lignitic. The 

 conflicting nature of the evidence is apparent, the 

 balance, apart from the botanical evidence, not here 

 referred to, being decidedly in favour of Tertiary age. 

 In the seventh chapter of the Annual Report, 1874, 

 Peale had already given, in tabulated form, the views of 

 authorities in regard to the age of each group of the 

 Lignites which have been referred to Tertiary. In a 

 much condensed form this might have been introduced 

 into the present Avork with advantage. None of the 

 Lignitic freshwater mollusca have been specifically iden- 

 tified with foreign forms ; the vertical distribution of 

 these being well-marked and limited, the evidence they 

 would present should be of great value. 



In this section (p. 24) a table is introduced incidentally^ 

 showing four groups of strata, .which, omitting the 

 lithology, the column of localities and all mention of 

 fossils other than vegetable, reads thus : — 



From this table we should certainly conclude that the 

 leaf remains were confined to the " Lignite group," and 

 consequently that the botanical part of the work referred 

 only to fossils of Eocene age. The work being on the 

 " Lignitic " we are still further confirmed in this opinion, 

 and dismiss the overlying "deposits," "group," and 

 "beds " from our minds. With this impression we come 

 to " Part II. Description of the Tertiary Fossil Plants,'" 

 and are in no way prepared for such a surprise as is 

 reserved for us in Part III., 273 pages further on, on 

 finding that the leaves are figured and described from beds 

 of Eocene, Miocene, and Pliocene age indiscriminately. 



In the second and third parts M. Lesquereux is evi- 

 dently working at more congenial subjects, and deserves 

 praise for the painstaking way in which he has described 

 the material before him. The truism that all determi- 

 nations based upon leaves alone are provisional and un- 

 trustworthy, has deterred English botanists from working 

 at our Tertiary floras ; and thus while we see magnificent 

 works on this subject brought out in France, Germany, 



