i6o 



SCIENCE. 



[Vol. XIV. No. 344 



the machine which would be liable to affect watches, etc., all the 

 field being contained within the outer iron shell forming the yoke. 

 Low speed in running is obtainable without increasing the size and 

 weight of the machine, and the whole is cheap to construct, and 

 combines features of mechanical strength and solidity with high 

 electrical efficiency. Finally, the machine is remarkably free from 

 any heating when running constantly and under full load. These 

 machines are manufactured by the Wenstrom Northern Electric 

 Company, of this city, of which Dr. J. B. De Lery is president ; 

 B. Blum, general manager, and B. J. Sturges, secretary and treas- 

 urer. This company intend to introduce their system for light and 

 power in the Eastern, Middle, and Western States. The Wen- 

 strom people have already installed during the past year several 

 thousand lights in Baltimore and Annapolis. 



THE NORTH AMERICAN MESOZOIC. i 



It has become customary upon such occasions as this for the 

 speaker to select a theme from subjects which he is supposed to 

 have specially studied ; and I have therefore chosen for mine the 

 mesozoic division of the geological record as it is exhibited on this 

 continent. This theme is so comprehensive that I propose only to 

 select from it certain topics which pertain to the distinguishing 

 characteristics of the principal subdivisions of the mesozoic that 

 have been recognized in different portions of North America ; to 

 their interdelimitation and to the delimitation of the division as a 

 whole from the carboniferous system beneath, and the cenozoic 

 above. I shall also make the discussion of these topics the oppor- 

 tunity of expressing certain views which I hold concerning them. 



To bring these discussions within the time allotted me they must 

 be confined to three general sections of the mesozoic formations, 

 one of which occurs within each of three regions of the continent, 

 namely, the Atlantic coast, the Pacific coast, and the interior re- 

 gions. Proceeding upon this plan, let us first consider the general 

 section which is to be observed in the Atlantic coast region. 



The rocks which in this region are now generally regarded as of 

 triassic age are found occupying limited isolated districts from 

 Prince Edward Island on the north to the State of South Carolina 

 on the south. If they extend further to the south, or south-west- 

 ward, they are covered from view by later formations. They are 

 found to rest unconformably upon various formations from the 

 archasan to the carboniferous inclusive ; except perhaps in Prince 

 Edward Island, where they are reported as resting conformably, or 

 nearly so, upon reputed Permian strata. Still, no intimate strati- 

 graphical or paleontological connection between the Permian and 

 the trias has been shown to exist there ; and the hiatus between 

 them is doubtless as great as it is farther southward, where the un- 

 conformity is so conspicuous. 



In this latter portion of the region it is evident that the great 

 uplift which involved the paleozoic rocks, including the reputed 

 Permian, took place long before the deposition of the earliest of 

 those triassic beds. These stratigraphical conditions indicate that 

 the hiatus in the geological record between the latest of the carbon- 

 iferous, and the earliest of the triassic deposits is equal to at least 

 the earlier half of the triassic, as that period is represented in 

 Europe. 



The only known paleontological evidence which appears to bear 

 upon this subject agrees with the stratigraphical indications just 

 mentioned. That is, the results of investigations by Professor 

 Newberry upon the fishes and plants of the strata in question, and 

 of Professor Fontaine upon the plants of the same, indicate that 

 they represent the later trias of Europe. But if triassic fishes had 

 not survived to the present day ; and if we knew more concerning 

 the developmental stages in the vegetable kingdom from the later 

 paleozoic to the later mesozoic inclusive, a good degree of uncer- 

 tainty which is naturally felt upon this point would doubtless dis- 

 appear. 



Our knowledge of the land vertebrate fauna which existed at the 

 time these deposits were formed is derived mainly from footprints ; 

 and it is therefore more than usually imperfect. The character of 



J Address before the Section of Geology and Geography of the American Associa- 

 tion for the Advancement of Science, nt Toronto, Ont-, Aug. 29, 1889, by Charles A. 

 White, vice-president of the section. 



this evidence as indicating triassic, rather than earlier Jurassic age, 

 seems to be far from unquestionable. 



Very few invertebrate fossils have been found in the trias of the 

 Atlantic coast region ; and the few that have been discovered are 

 of little or no value as indicating the age of the strata containing 

 them. 



As to the relation of these deposits with the carboniferous sys- 

 tem, only stratigraphical evidence has thus far been obtained, and 

 this shows only the bare fact that the former are of considerably 

 later age than the latter. That is, no direct, or even approximately 

 close, biological relationship between them has yet been discovered, 

 the biological hiatus being apparently quite as great as the strati- 

 graphical one. It may be mentioned here also that we have no 

 evidence that the trias of the Atlantic coast was ever continuous, 

 or that it was exactly contemporaneous, with the reputed trias of 

 the interior region, which will be presently referred to. 



Intermediate between the triassic beds and the undisputed cre- 

 taceous deposits of the Atlantic coast region there is a series of 

 strata, evidently of littoral and estuary origin, but, at least in part, 

 of doubtful age, to which the name of Potomac formation has been 

 applied. These deposits reach at most only a few hundred feet in 

 thickness, and although frequently covered from sight by later for- 

 mations, they seem to have been originally continuous from New 

 Jersey to the State of Mississippi. They have no known represen- 

 tative west of the Mississippi River, unless it shall be shown that they 

 are represented by some sandy beds at the base of the Texas cre- 

 taceous section. These Potomac beds are usually found resting 

 upon the archasan, and at only a few points are they found to rest 

 directly upon the triassic rocks, when they are plainly uncomform- 

 able. They seem to be constantly present beneath the marine cre- 

 taceous strata just mentioned, and no representative of another 

 formation has yet been observed between them. 



Invertebrate fossils are exceedingly rare in the Potomac forma- 

 tion, and the few that have been found give no direct indication of 

 its geological age. Professor Whitfield, however, has suggested 

 that the Raritan clays, together with the Amboy clays, which by 

 some geologists are included in the Potomac formation, but which 

 are probably of later date, are of Jurassic age because of the simi- 

 larity of his new lamellibranchiate genus Ambonicardia with cer- 

 tain European Jurassic shells. 



Large collections of fossil plants have been obtained from the 

 deposits here provisionally grouped together under the name of 

 Potomac formation, at numerous and widely separated localities. 

 These collections differ so greatly in character from one another 

 that it seems necessary to infer that more than one flora is rep- 

 resented by them. Many years ago Dr. Tyson found some fossil 

 plants in Maryland which he regarded as of Jurassic age, and which 

 closely resemble certain forms that are found in the European Jura. 

 Professor Ward, in reviewing the large flora which Professor Fon- 

 taine has published from the Potomac formation in Virginia, and 

 having in mind also the Maryland plants just referred to, recog- 

 nizes the Jurassic character of several of the species, according to 

 the European standard, but he takes the rational ground that all 

 obtainable evidence ought to be considered before reaching a final 

 decision as to the true age of the deposits containing them. 



Professor Newberry, who has made extensive studies of the plant 

 remains of the Raritan and Amboy clays, finds among them none 

 that give any indication of their Jurassic age. On the contrary, he 

 finds that the flora of those clays as a whole indicates that they 

 ought to be referred to an epoch not later than the middle cre- 

 taceous of Europe, nor probably earlier than the upper neocomian. 



Professor Marsh has published some dinosaurian remains from 

 apparently the same horizon in the Potomac formation that furnished 

 the plants to Dr. Tyson and Professor Fontaine, which he has re- 

 ferred to the Jurassic. 



Paleontological testimony being thus conflicting in its character, 

 one naturally infers that more than one epoch is represented by the 

 deposits that now bear the common name of Potomac formation ; 

 but I shall presently call your attention to some cases of commin- 

 gling of earlier and later moUuscan types in one and the same 

 formation which are quite as remarkable as this apparent com- 

 mingling of diverse plant and vertebrate types in the Potomac 

 formation. 



