52 



BOOK REVIEWS 



The Laramie Flora* 



After many and vexatious delays, Knowlton's revision of the 

 Laramie Flora has at last made its appearance. I saw the 

 practically completed manuscript years ago, and it is regrettable 

 that works of this kind cannot be issued with reasonable 

 promptness after being submitted for publication. 



Now that we have the book it is all that could be expected, 

 forming an excellent foundation on which to build further work 

 dealing with the fascinating problem of the uppermost Cretaceous 

 floras, and their relation to those of the lower Teritary. The 

 exceedingly complete historical summary shows us clearly how 

 the essential facts, often obscured by mistakes and misunder- 

 standings, have gradually taken shape, so that to-day it is pos- 

 sible to distinguish what is evidently a single flora, and discuss 

 its characters and relationships. This flora indicates warm and 

 moist conditions but is very different from the present neotropical 

 region. The great representation of Fie us, with about 40 

 species is a salient feature. Stanley enumerates 23 valid species 

 of Ficus from Mexico to-day, and 41 from Mexico and Central 

 America combined, but these would not be found together in 

 a flora as restricted as the Laramie presumably was. Berryf 

 has lately pointed out the probability that several of the "species" 

 of Ficus represent variations of a single type and has proposed 

 to unite at least two of the Laramie species with the Eocene 

 F. mississippiensis (Lesq.) Berry. This may perhaps be correct 

 but while it is certainly true that diverse appearing leaves may 

 even come from a single tree, it is probable on the other hand, 

 that the Cretaceous and Eocene plants, if we knew them per- 

 fectly, would prove to be different. The subject is a large and 

 difficult one, but we may doubtless get some light on the rate 

 of modification of specific types, not only from fossils but also 

 from a study of geographical distribution, particularly on islands. 



Under F. navicularis Ckll. Knowlton remarks that it is 

 doubtless different from F. lanceolata Heer of the Swiss Miocene. 



* The Laramie Flora of the Denver Basin, with a Review of the Laramie 

 Problem. F. H. Knowlton, \}. S. Geological Survey, Professional paper 130. 

 175 pp., 28 plates. 1922. 



t Additions to the Flora of the Wicox group. U. S. Geol. Survey, Prof. 

 paper 131-A. 1922. 



