340 



SCIENCE. 



[N. S. Vol. I. No. 13. 



fore important to note in what proportions 

 these 14 genera occur in the two floras : 



GENERA COMMON TO AMERICAN TRIAS AND JU- 

 RASSIC OF PORTUGAL. 



Baiera 



Brachyphyllum 

 Cheirolepis . 

 Chondrites . 

 Cladophlebis 

 Clathropteris 

 Equisetum . 

 Otozamites . 

 Pagiophyllum 



NUMBER OF SPECIES. 



Pecopteris . 

 Podozamites 

 Schizoneura . 

 Voltzia . . . 



When we consider that the two horizons 

 do not at all overlap and that more than 

 three-fourths of the Portuguese plants come 

 from the uppermost members of the Juras- 

 sic, it is not to be expected that the corre- 

 spondence mil be very close ; and accord- 

 ingly we not only miss in the Portuguese 

 flora some of the largest American genera, 

 such as Aci-ostichites, Ctenophyllum, and 

 Pterophyllum, but also some of the most 

 striking and abundant forms, such as Macro- 

 tseniopteris, while on the other hand no 

 monocotyledons occur in the American 

 Trias so far as known, and the two largest 

 genera of ferns in the Portuguese Jurassic, 

 Sphenopteris and Scleropteris, are entirely 

 wanting in the American Trias. 



THE CRETACEOUS FLORA. 



The Cretaceous flora of Portugal has 

 much greater interest for the student of 

 American paleobotany than the Jurassic 

 flora, which has just been considered. 

 First, because, as now known, it is consid- 

 erably larger, numbering 199 species, but 

 chiefly because we have in America a large 

 number of plant bearing deposits that cor- 

 respond so closely with those of Portugal 

 that a comparison may be legitimately 



made that furnishes valuable results. It is 

 true that our American Lower Cretaceous 

 flora has now been so extensively worked 

 that it has assumed relatively large propor- 

 tions, numbering, so far as known, over 

 800 species. The Potomac formation alone 

 furnishes no less than 737. The interest is 

 stDl further heightened by the fact that in 

 the Lower Cretaceous of both Portugal and 

 America, the plant bearing beds occur at a 

 number of distinct horizons, which may not 

 without profit be directly compared in the 

 two countries. For example, the Potomac 

 formation now furnishes at least five distinct 

 horizons from which fossU plants have been 

 obtained, the lowest being that of the James 

 Eiver, which may extend as low as the top 

 of the Jurassic. The next higher is that so 

 well known at Fredericksburg, A'irginia, 

 and other points on the Eappahannock and 

 Potomac Rivers. The third is the Mount 

 Vernon clays which directly overlie the 

 last named and have furnished a distinct 

 flora. The fourth is well developed in the 

 vicinity of Aquia Creek, the plant bearing 

 beds near Brooke, Virginia. The fifth is 

 undoubtedly much higher, and there appeai-s 

 to be a considerable thickness of non-fossil- 

 iferous deposits intervening between the 

 last named and those plant bearing beds 

 that have been discovered on the eastern 

 side of the District of Columbia and at 

 other points near Washington, on the 

 Severn River, and on the Eastern Shore of 

 the Chesapeake Bay, which have furnished a 

 flora substantially identical with that of 

 the Ambojr clays on the Raritan River and 

 of Staten Island, Long Island and Mar- 

 thas Vineyard, as well as of the Tuscaloosa 

 formation of Alabama. 



The Lower Cretaceous of Portugal is sub- 

 divided into a very similar series of plant 

 bearing deposits. One locality, Valle-de- 

 Brouco, is referred by Chofiat to the In- 

 fravalanginiau, which is at the veiy base of 

 the Neocomian and corresponds well with 



