414 



SCmNGE. 



[N. S. Vol. V. No. 115. 



studies of the formation in that State that 

 he thought the cycads came from the sand- 

 stone member, and he once took me to see 

 what he regarded as a typical exposure, on 

 the Patapsco, near Eelay, of the basal ar- 

 kose, identical with certain phases that it 

 presents in Virginia. This observation has 

 been abundantly verified. 



In common, however, with the prevailing 

 opinion at that date, which was shared by 

 Mr. McGee and mj'self, he regarded the iron 

 ore clays, so-called, as somewhat higher 

 and as constituting an ' Upper Clay Mem- 

 ber.' At that time no other fossils than 

 cycads, silicified wood and lignite had been 

 found in the iron ore belt. Within the last 

 two years, however, Mr. Arthur Bibbins 

 has demonstrated the occurrence of fossil 

 plants representing a considerable variety, 

 but chiefly consisting of ferns and conifers. 

 He finds them not only in the iron ore de- 

 posits, but in the iron ore itself, and I have 

 had the satisfaction, in company with him, 

 of collecting a large number of these and 

 also of examining the much larger collec- 

 tion which he has made. Although these 

 collections have not yet been elaborated 

 and fully determined, a simple glance 

 at them would be sufficient to show that 

 they represent a flora substantially identi- 

 cal with that of the basal Potomac in Vir- 

 ginia, as typified in the Fredericksburg de- 

 posits. At the same time that Mr. Hatcher 

 collected the bones in these beds which 

 were described by Professor Marsh, and 

 which constitute the only paleontological 

 evidence that he has thus far brought for- 

 ward as to their age, he also obtained, in 

 intimate association with the vertebrate re- 

 mains, a large number of fossil cones, which 

 belong to the genus Sequoia and were un- 

 doubtedly borne on the trees which have 

 furnished the silicified wood. All this is 

 simply confirmatory of the antiquity of the 

 iron ores and of their substantial identity 

 in age with the basal Potomac of Virginia. 



Professor Fontaine's general conclusions 

 as to the stratigraphical relations of the 

 Potomac formation are of such value in 

 connection with the views of Dr. Newberry, 

 next to be considered, that they should be 

 given somewhat in extenso. They are to be 

 found on pages 143-147 of this Bulletin: 



"The New Jersey beds, as is shown by 

 their fossil plants, are certainly considerably 

 younger than the Virginia member of the 

 Potomac. So far as is yet known, the 

 Ambo}' clay is not younger than the Ceno- 

 manian of Europe. 



' ' So far, then, as can be determined by the 

 stratigraphy, the Virginia Potomac is con- 

 siderably older than the Cenomanian and 

 much younger than the Rhetic. The evidence 

 from the stratigraphy, so far as it goes, 

 agrees well with that of the fossils found 

 in the Potomac. 



" The Wealden formation is most probably not 

 uppermost Jurassic, but the estuary and marsh 

 equivalent of the oldest marine Neocomian. 

 What will be said therefore concerning the 

 Neocomian will include the Wealden. 



" The flora of the Potomac seems to have 

 been an abundant one. It was rich in 

 species of certain groups, but, as compared 

 with modern floras, it was poor in types. A 

 large amount of fossiliferous material was 

 obtained from points located at intervals be- 

 tween James River and Baltimore. The 

 fossils found will give a fair idea of the 

 general character of the flora. This flora 

 has been studied by me, and is described in 

 Monograph XV of the United States Geo- 

 logical Survey. The comparison of these 

 plants with those of known fossil floras 

 shows somewhat complex relations. 



" There is present in the Potomac flora a 

 Jurassic element which is large in the very 

 considerable number of genera that char- 

 acterize that system. Some few of the 

 genera begin as far back as the Rhetic. This 

 element shows indications of decadence. 

 The number of species of each genus is 



