I 

 582 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



also finds the shells of Rudistes and bivalves: Lucina, Cardium, Pecten, Ostrea, Exogyra ious- 

 singaulti d'Orb.; of echinoderms : Ananchytes ovata Lam., Micraster cor-anguinum Goldf., 

 Discoidea excentrica d'Orb., Echinus iolivarii d'Orb., Enallaster Tcarsteni de Loriol, Galerites 

 sp., etc. This group of siliceous rocks, whose thickness may be estimated roughly at 1,000 

 meters, usually forms the summits of the eastern chain. The Paramo de Chita, which has an 

 altitude of about 6,000 meters and is covered with eternal snow, [and other summits] are formed 

 of these sandstones and siliceous shales. The beds which carry Polythalamies are uncon- 

 formably overlain by micaceaus sandstone which is either white or yellow and more or less 

 coarse, or by sandstones and variegated marls containing beds of lignite. 



This last group is assigned by Karsten to the Tertiary and further description 

 of it is given in Chapter XVII (p. 796). 



The geologic constitution of the Cordillera of Bogota was described in 1892 

 by Hettner/'^ who distinguished several divisions of the Cretaceous as follows: 



Although various explorers have from time to time collected fossils, we are indebted par- 

 ticularly to Karsten for an attempt to distinguish the sedimentary rocks of Colombia. He 

 separated Lower Cretaceous or Neocomien, Middle Cretaceous or Gault, which appears with 

 two definite variations. Upper Cretaceous, and Tertiary. The classification which I have 

 adopted during my journeys agrees in general with Karsten, and Sievers has adopted approxi- 

 mately the same classification for the Cordillera of Merida in Venezuela. 



The characteristic rock of the Neocomien is, according to Karsten, a sandy light-brown or 

 red-yellow, imperfectly stratified marl with interbedded strata of blue or dark-colored lime- 

 stone which predominates in the upper portions. Karsten found fossils in one locality only, 

 near Caqueza. I must admit that I have not discovered any and that I therefore must classify 

 this formation with the following one, the Gauit, inasmuch as they are not particularly differ- 

 ent in lithologic character. The Lower Cretaceous (Neocomien and Gault) is therefore in 

 general a thick series of clay slates, shales, and bright-colored shaly clays, which are inter- 

 bedded witn thick strata of blue or more rarely black or white limestone, white quartzite, and 

 white, sometimes reddish and greenish sandstones, as well as some other subordinate strata. 

 Where they possess the typical character I propose to call them the VUletas formation, and the 

 greater part of the limestones of the Middle Cretaceous which Sievers has distinguished in his 

 profile sections probably. The principal part of the Villetas formation has been determined 

 by Steinmann as Urgo-Aptien on the basis of its fossils ; whereas the upper strata belong to the 

 true Gault. 



In the vicinity of Jiron and Zapatoca and elsewhere there occurs, in the neighborhood of 

 the granite gneiss and porphyry, clay, reddish or white, and in part greenish sandstone which, 

 together with violet-brown shales and reddish sandstones may be named the Jiron formation. 

 This is the reddish-yellow sandstone which Karsten regarded as a special development of the 

 Neocomien, and although there are fossils I would also class it as a portion of the basal Cretaceous 

 that is peculiarly characterized through proximity to the crystalline rocks. Sievers also regarded 

 this formation, which occurs apparently quite frequently in the Cordillera, as the lowest mem- 

 ber of the Cretaceous. Elsewhere, especially in the snow-covered mountains of Cocui, a 

 white quartzite which usually occurs only in thin beds in the slates and clays becomes so thick 

 that it replaces all other rocks. This Cocui quartzite probably corresponds to the Uribante 

 sandstone of Sievers. The blue limestone may, however, become the predominant member 

 and entirely replace the slates and clays, as is the case in the neighborhood of Velez. 



Toward the top the ViUetas formation appears to pass by gradation into the next division, 

 the Guadalupe (Karsten's Upper Cretaceous). The slates and shales become less frequent and 

 occur only as thin interbedded layers. The greater part of this division is siliceous sandstone 

 or a thm-bedded sUicified clay rock, together with a heavy-bedded white quartz sandstone 

 which in general overlies the other strata. Fossils are very rarely found and are not such as 

 may be definitely determined. It is therefore doubtful whether the Guadalupe formation 

 belongs to the Gault or to the Upper Cretaceous. 



