THE HALLOPUS, BAPTANODON, AND ATLANTOSAURUS 

 BEDS OF MARSH 



S. W. WILLISTON 



The University of Chicago 



HALLOPUS BEDS 



In the American Journal oj Science for October, 1891, Professor 

 O. C. Marsh proposed the name "Hallopus beds" for a somewhat 

 indeterminate horizon of vertebrate fossils, as follows: 



Near the base of the Jurassic a new horizon may now be defined as the Hallopus 

 beds, as here alone remains of the remarkable reptile named by the author Hal- 

 lopus victor have been found. Another diminutive dinosaur, Nanosaurus, occurs 

 in the same strata. The horizon is believed to be lower than the Baptanodon 

 beds, though the two have not been found together. The Hallopus beds now 

 known are in Colorado, below the Atlantosaurus beds, but quite distinct from 

 them. 



The Baptanodon beds have been found in many localities everywhere beneath 

 the Atlantosaurus beds, and having below them, at various localities, a series of 

 red beds, which may, perhaps, contain the Hallopus horizon, but are generally 

 regarded as Triassic. 



This reference of Marsh to a vertebrate horizon below the marine 

 Jurassic of the Rocky Mountain region has been wholly overlooked 

 or disregarded by subsequent writers, the fauna itself having been 

 referred to the "Upper Jura." I am now in a position, I believe, 

 to show that the horizon is a distinct one, and that it belongs, not to 

 the Lower Jurassic, but to the Upper Triassic. I, furthermore,, 

 believe that the horizon will eventually be found to be widely fossil- 

 iferous in the Rocky Mountain region. 



Although I cannot be entirely sure, after so long an interval, 

 it is my recollection that the type specimen of Hallopus victor was 

 discovered by Mr. M. P. Felch in August, 1877, in Garden Park, 

 near Canon City, Colo., a few weeks before the time of my first 

 visit to that since famous locality. The precise spot whence the 

 specimen came was pointed out to me, the base of an escarpment of 

 red sandstone, whither the specimen had fallen from the overhanging 



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