Reviews. 



Monographs of the U. S. Geological Survey, vol. XVII. The Flora of 



the Dakota Group. A posthumous work by Leo L-esquereux. 



Edited by F. H. Knowlton. 256 pp., 66 plates. Washington, 

 1892. 



The posthumous issue of this product of many years of labor, 

 including some of the best work of one who for many years was distin- 

 guished as the highest authority in American paleobotany, is a mat- 

 ter of great interest to both paleontologists and biologists, since it 

 renders the plant remains of the Dakota group, one of the oldest dico- 

 tyledon-bearing terranes, the most completely -elaborated and best- 

 known flora, perhaps without exception, of any restricted formation in 

 the world. Within its two hundred and fifty- six quarto pages, four hun- 

 dred and sixty species are described, or, in the case of those concern- 

 ing which no new observations had been made since the publication of 

 his '■'Cretaceous Flora'" and ''■Cretaceous and Tertiary Floras,''' enume- 

 rated with references to his earlier works. The drawings, a considera- 

 ble number of which were unfinished at the time of the author's death, 

 occupy sixty -six plates. 



Of the flora, as a whole, over ninety per cent, are dicotyledons, one 

 and three - tenths per cent, ferns, three and one - half per cent, conifers, 

 and two and one -half per cent, cycads. In this overwhelmingly dico- 

 tyledonous flora, most of our American living tree- families have their 

 representatives. While going over the descriptions and figures it will 

 seem to some readers that the number of species, and particularly of 

 varieties, is, in some instances, too great, there being for example, four 

 varieties of Salix protecefolia, seven of Viburnum lesquereuxii, and fif- 

 teen of Betulites Westii, especially since we are left to infer in the latter 

 case that all have the same rather indefinite habitat, " Ellsworth County, 

 Kansas." But, while it is probably true that some of the variations do 

 not vary more than the leaves on a single tree, still it should be borne in 

 mind that that period in the history of the dicotyledons, soon after their 

 first appearance in the Cretaceous, was one of immense diversity of 

 form and great modification of character; and, although, as Professor 



300 



