March 12, 1897.] 



SCIENCE. 



419 



Dakota group can be much more definitely 

 determined, for the proportion between the 

 angiosperms and the lower plants in the Da- 

 kota group is about the same as in theAmboy 

 Clays, showing a similar stage of progress in 

 the development of plant life. "We have 

 already obtained 12 species common to the 

 two formations, a number that will undoubt- 

 edly be considerably augmented with the 

 further exploitation of the Amboy flora. 

 Tlie Dakota group is hnoivn to occupy about the 

 middle of the Cretaceous system. Until recently 

 it was supposed to be the basal member of 

 that system as developed on the North 

 American continent, and it was believed 

 that until about the middle of the Creta- 

 ceous period our continent had remained 

 above the ocean level ; but it has been shown 

 recently that considerable areas of North Amer- 

 ica are occupied by sediments deposited from the 

 Cretaceous sea before the date of the Dakota 

 formation, and that on the northwestern 

 coast, on Queen Charlotte Island, and in the 

 Shasta group in California we have accu- 

 mulations of sediment that took place before 

 the Dakota sandstones. Mr. E,. T. Hill and 

 Dr. C. A. White have demonstrated that a 

 considerable portion of the State of Texas is 

 underlain by rocks that are the equivalent of 

 the Neocomian or Lower Cretaceous of the Old 

 World. Very recently, too, Sir William Daw- 

 son has found in the fresh- water coal-bear- 

 ing deposits of western Canada fossil plants 

 identical with some from the Kome group or 

 Lower Cretaceous of Greenland ; and a much 

 larger collection of fossil plants obtained 

 by the writer from the coal basin of the 

 Falls of the Missouri in Montana, collected 

 by Mr. E. S. Williams, contains many 

 Kootanie or Lower Cretaceous plants, and, 

 what is of still greater interest, a number 

 of species that have been described by Pro- 

 fessor Fontaine from the Potomac group of 

 Virginia. Thius the conclusions of Professor 

 Fontaine as to the Wealden age of the Potomac 

 are strikingly confirmed. His arguments in 



favor of this view were that the Potomac 

 flora was most like that of the Wealden of 

 Europe, a few of the species being apparently 

 identical, while it had nothing in common 

 with any other flora known. To this I ven- 

 tured to add the suggestion that it could hardly 

 be Jurassic, as claimed by some writers, since 

 in no part of the world had angiosperm plants 

 been found in the Jurassic, though in Europe 

 the Jurassic rocks had yielded great numbers of 

 plants and the flora had been carefully studied. 

 Now the finding of species identical with 

 those of the Potomac in the Great Falls 

 basin, and with them plants found in the 

 Kootanie of Canada and the Kome deposits 

 of Greenland, seems to place the question 

 beyond doubt." 



He was struck by the fact that several 

 species were identical with those long ago 

 discovered at Aachen by Dr. Debey, oc- 

 curring in a formation whose geological 

 position is known to be Upper Cretaceous, 

 and he took the trouble to visit that locality 

 and examine Debey's collections, a consid- 

 erable number of which he purchased and 

 brought to America. After carefully com- 

 paring these with those of the Amboy Clays, 

 and in the light of an extensive acquaintance 

 with other similar floras, he concludes the 

 introductory part of his work with the fol- 

 lowing general statement (p. 33): 



" The mode of accumulation of the beds 

 at Aachen seems to have been similar to 

 that of the Amboy Clays and the Potomac 

 group ; that is, they are local estuarine beds 

 resting upon the Paleozoic rocks and com- 

 posed of the wash of the neighboring land, 

 in which were buried great numbers of 

 leaves and trunks of the trees which grew 

 upon that land. The trunks are now con- 

 verted into lignite, and they are as conspic- 

 uous an element in the lithology of the 

 group as in New Jersey. Dr. Debey sup- 

 posed that his collection contained 300 to 

 400 species of angiosperm plants. This is 

 perhaps an exaggeration, for he included in 



