204 TEN years' progress in vertebrate paleontology 



Further, when these studies can be extended to include the beds and 

 the fossils of the deposits of the closing Paleozoic all ovei the world, it 

 will be possible to determine the effect of climate on the development, 

 notably the great glaciation of the southern hemisphere, and we can test 

 Broom's suggestion that the reptiles, at least, originated in the north cen- 

 tral portion of South America and from thence spread over the world. 



The peculiarities of the fauna, the promise of abundant material, the 

 possibility of making definite determination as to the climate and the 

 conditions of deposition, give us a splendid chance to work out the laws 

 governing the development of groups which have completed their cycle. 

 The laws of decadence, even to extinction, will be as clearly illustrated as 

 the laws of progressive development to an optimum, such as we can see in 

 other and more recent groups. 



JURASSIC DINOSAURS 

 BY W. J. HOLLAND 



Without entering into the merits of the discussion which has long been 

 pending as to the geological age of the Wealden, the Potomac beds, and 

 other measures which are claimed b}^ some as being Jurassic, by others as 

 belonging to the Cretaceous, I may state that there appears to me to be 

 reason to strongly maintain, as has been done hy Professor Marsh and 

 others, that the formations known in America as the Morrison beds and 

 as the Como, or Atlantosaurus beds, are truly referable to the Jurassic. 

 The discovery by Mr. J. B. Hatcher at Canon City of the saiTTopod dino- 

 saur, to which he gave the name of Haplacanthosaurus, and which is so 

 closely related to the Cetiosaurus of Owen, coming from the Oxford clays, 

 as to be scarcely distinguishable from it, seems to establish beyond ques- 

 tion the fact that the beds at Canon City are Jurassic. Associated with 

 the remains of Haplacanthosaurus were found the remains of Diplodocus, 

 Morosaurus, and Stegosaurns. Kow, while the horizons explored by 

 Marsh and Hatcher at Caiion City are probably a little lower than the 

 Morrison or the Como beds, nevertheless the existence in these latter for- 

 mations of the identical genera, and apparently the same species, indi- 

 cates very clearly that these beds also are referable to the Jurassic, coming 

 very near to the top of the series, being overlaid in Wyoming, in Colorado, 

 and in Utah by the Dakota sandstones of the Cretaceous. The strata 

 revealed in the quarry in Uinta County, Utah, which has been worked by 

 the Carnegie Museum during the past three 3'ears, show relationships to 

 the measures above and below them, coinciding exactly Avith what we find 



