HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 69 
Wealden, with which Marsh had been in favor of correlating them and which was 
-at that time very generally regarded as of Upper Jurassic age though at present 
considered by most geologists as representing the lowermost member of the Creta- 
ceous. 
Professor Lester F. Ward, on page 377 of Part IL. of the Twentieth Annual 
Report of the United States Geological Survey, in commencing his treatise on the 
Jurassic cycads dismisses the age of these beds as developed in Wyoming with the 
remark that there is no doubt as to their being Jurassic, and on page 384 he says 
of the cycads from the Freeze Out Hills locality that “in some respects they resem- 
ble the specimens from the Purbeck beds of the Isle of Portland.” 
Professor Wilber C. Knight’ has remarked as follows concerning the age of the 
Atlantosaurus (Como) beds. ‘There can be no mistake in assigning the Como stage 
to the Upper Jurassic, but it seems quite possible that it is more closely allied to the 
Purbeckian than to the Oxfordian.” 
Darton” is not very clear as to just what age he wishes to refer these beds. In 
his diagram at the top of page 387 of the paper just cited he refers them to the 
‘Lower Cretaceous (or Jurassic)?”’ and immediately after on the same page in his 
table of the thickness of formations, and again on page 393 in describing the charac- 
ter and distribution of the Atlantosawrus beds (Beulah Shales) he refers them to the 
Jurassic without a query. It would seem therefore that he also favored their 
Jurassic age. 
Osborn has I think consistently maintained the Jurassic age of these deposits. 
On the other hand Scott and Williston have been in favor of placing them in the 
Lower Cretaceous. 
As already noticed Dr. C. A. White has regarded these beds as of Jurassic age 
though apparently relying entirely upon the evidence afforded by the vertebrates 
and remarking that the fresh-water invertebrates of the same beds are so modern in 
type as of themselves to offer no suggestion of a greater age than Tertiary. And 
again he adds: ‘Indeed so modern is the facies . . . that one is surprised to find 
only a single type among them which is not common among American living fresh- 
water species.” 
In discussing the age of any geological horizon which is fossiliferous two classes of 
evidence are of especial importance. First in importance is its stratigraphic position 
and second the nature of its included fossils, vertebrates, invertebrates and plants. 
The relative value of the different classes of fossils for purposes of correlation vary 
” Bull. Geol. Soc. Am., Vol. 11, p. 387. 
" Bull. Geol. Soc. Am., Vol. 10, pp. 387, 398. 
