258 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



As a further proof of the fact that the continental land masses were 

 large and extensive during the Jurassic period, we have the indisputable 

 testimony that on the Pacific coasts of both the North and South 

 American continents there is an extensive development of fossiliferous 

 marine littoral Jurassic beds, which grade up without break into the 

 Cretaceous formations of the Pacific province which were deposited 

 against a land barrier. 



Furthermore, it is very probable that the Pacific shore lay much 

 farther to the eastward during this period than at present, for, as will be 

 shown in our discussion of the Cretaceous, beds of Pacific sedimentation 

 occur in the Mexican peninsula at Catorce, far eastward of the present 

 Pacific shore line. These beds were undoubtedly derived from an east- 

 ward lying land, and the Pacific at the beginning of the Cretaceous 

 epoch covered a large portion of the Mexican region. 



Fossiliferous Jurassic beds are now known to occur on the western 

 or interior side of the Eastern Cordilleras in Mexico and Trans-Pecos, 

 Texas, at Catorce, as noted by Aguillera, Miquehuana and Monterey, as 

 seen by the writer, and at Malone, Texas, as recently reported by 

 Cragin. The oceanic affinities of these beds are as yet unpublished, but 

 geographically they belong to the great interior basin region, and not 

 the Atlantic slope. 



A. Agassiz has shown that the deep-sea echinoid fauna of the Carib- 

 bean and Gulf of Mexico contains a mixture of Mesozoic Pacific types. 

 This fact may suggest that there was an oceanic passage across Central 

 America in Jurassic time, and that the continental bridge, if it existed, 

 may have then been in the Windward region. The discussion of this 

 conjecture, however, must be postponed until a future paper. 



The Cretaceous. — The records of the Cretaceous period also present 

 evidence which suggests a possibility of the existence of a complete land 

 barrier between the two oceans. The Cretaceous rocks are highly fos- 

 siliferous, and are the first in ascending series affording sufficient pale- 

 ontologic data upon which to base a discussion of the past relations of 

 the two great oceans. 



Discordance of the Faunas of the Atlantic ami Pacific Provinces. — Active 

 research of recent years has resulted in the conclusion that, of the many 

 hundred species occurring in the large faunas of the Lower and Upper 

 Cretaceous sediments of the Atlantic and Pacific provinces of the United 

 States, not one species has been found in common with the faunas of the 

 two oceans. So marked is this difference that it is the most impressive 

 fact which has been encountered by recent students of these forma- 



