174 BULLETIN: MUSEUM OF COMPAKATIVE ZOOLOGY. 



beds of Costa Rica,' are of a clastic nature, and intermixed with volcanic 

 debris, and contain a little studied fauna of Rudistes quite suggestive of 

 the Antillean type. The oldest known formation of Panama is an un- 

 fossiliferous andesitic tuff of Pre-Tertiary and probably Cretaceous age. 



iS^o Cretaceous formations interbedded in igneous deposits analogous 

 to these are known to exist on the coast of the North American conti- 

 nent north of Tehuantepec, although, as has been shown, active vul- 

 cauism was in progress during the Upper Cretaceous period in the 

 vicinity of Austin, Texas, and southwestward. Whether or not this 

 was the most northern extent of the volcanic phenomena which were 

 especially active throughout the Central America, Isthmian, Antillean 

 Andean, and Venezuelan regions at that time cannot be stated. 



The northern portions of the South American continent — Colombia, 

 Venezuela, and the outlying islands of the Venezuelan seaboard — pos- 

 sess Cretaceous faunas of a South American type, including beds of older 

 epochs than those foimd in Jamaica. Pteroceras, Cerithium, Turritella, 

 Trigonia subcrenulata. Area, Cardium, and Echinus have been reported 

 by the official Trinidad Survey^ from Cumana, on the mainland near 

 Trinidad. 



Stratified formations of the type of the Richmond beds, composed of 

 impure land derived carbonaceous shales and sandstones grading upward 

 into calcareous beds representing the initiative of the great Mid-Ter- 

 tiary subsidence, also have wide occurrence in the West Indies, although 

 but few attempts have been made at differentiating them from the pre- 

 ceding group with which they are continuous. 



In San Domingo and Haiti, as in Jamaica, this formation undoubt- 

 edly has extensive development. It has been clearl}^ described by Gabb,^ 

 but confused with the equivalents of the Bowden beds. It is most 

 probable that the uptilted coarse sandstones, conglomerates near Bao 

 and Yagui, and the shales into which they grade as described by him, 

 are the equivalents of the Richmond beds. They have a thickness 

 between 1,200 and 1,500 feet. Tippenhauer's * description of the 

 Eocene conglomerates of Haiti conforms perfectly with the nature of 



1 Geological History of the Isthmus of Panama and Portions of Costa Rica. 

 Based upon a Reconnoissance made for Alexander Agassiz, by Robert T. Hill. 

 Bull. Mus. Comp. Zoiil., Vol. XXVIII. No. 5, 1808, pp. 226, 227. 



2 Report on the Geology of Trinidad, by G. P. Wall and J. G. Sawkins, London, 

 18G0, p. 106. 



3 Op. cit., p. 94. 



* Op. cit., pp. 85, 86. 



