REVIEWS. 301 



Lesquereux himself suggested, their dii^erentiation might, under other 

 circumstances, be "hazardous," yet the discrimination of the forms 

 furnishes a better paleontological basis for the interpretation of mod- 

 ern types, as well as a higher degree of definition, for the use of pale- 

 ontological stratigraphy. 



At the close of the memoir, the broad range of the author's knowl- 

 edge and paleobotanical experience is well shown in some thirty pages, 

 devoted to an "Analysis" of the flora of the group. From this analy- 

 sis, which is of great value to the biological paleontologist, he reaches 

 the conclusions that, although but one - fourteenth of the species found 

 in the Dakota group are also found in the Atane beds of Greenland, 

 yet, considering the remoteness of the regions, the close relationship 

 of the floras, and the difference in latitude, and, perhaps, in soil, the 

 proofs are "really conclusive" of the synchronism of the two forma- 

 tions ; " that most of the types of the arborescent flora of North America 

 were present in that of the Dakota group, and that most of them had 

 left remains of allied specific or generic forms in the intermediate 

 periods," so that the flora of this continent is indigenous ; and that 

 "all the plants of the American Cenomanian, except those of Ficus and 

 Cycads," which, he explains, may be omitted, "might find a congenial 

 climate in the United States between 30° and 40° of latitude," a con- 

 tinued uniformity of climate, causing "the preservation of the original 

 types of the flora, subjected to some modification of their original 

 characters, without destroying them or forcing their removal by the 

 introduction of strange or exotic forms." 



Although a great proportion of the species found in any given locality 

 are not reported from any other point, it will readily be understood 

 why no attempt is made to work out any floral horizons in the Dakota 

 group, when the reader observes that, while a portion of the species are 

 reported from among a dozen localities, and a few specimens come 

 from Minnesota and Nebraska, owing to the circumstances attending 

 their collection and accumulation in Professor Lesquereux's hands, a 

 large part, perhaps the greater number of them, have no more restricted 

 habitat than "Ellsworth County, Kansas," or merely "Kansas." It is 

 noted, however, that in one or two instances no change in the associa- 

 tions of the species was met in descending fifty or seventy -five feet in 

 the series. The geological interest of the work would have been fur- 

 ther increased if collections from the southwestern extension of the 

 group had also been made and studied with the rest. 



