HORIZONS OF VERTEBRATE FOSSILS. 475 



p \i;t i. 



GEOLOGICAL HORIZONS. 



The base "I the Mesozoic in the Denver Basin appears ii> be repre- 

 sented by certain red sandstones, which rest directly againsl the Archean. 

 No characteristic vertebrate fossils have \<'i been found in these strata, and 

 tlu-v have usually been classed with the overlying Jurassic beds, under the 

 general name of Juratrias. Farther to the south in New Mexico, and 

 especially to the southwesl in Arizona, this series of sandstones or their 

 equivalents in position contain vertebrate fossils, and among these the 

 writer has recognized both dinosaurian and crocodilian remains of Triassic 

 types. Future exploration in the Denver region and in the same horizon 

 farther south may bring to light characteristic fossils and determine mon 

 accurately the age of these interesting deposits. 



JUEASSIC. 



HALLOP1 - i 



Immediately over the sandstones above mentioned is a large series of 

 str;it;i which are undoubtedly Jurassic in their upper portion, and perhaps 

 throughout. Near the base of this series in the Canyon region are the 

 Hallopus beds, as indicated in the section in fig. 23. These beds are of 

 special importance biologically, owing to the fad thai they contain remains 

 <>t' the smallest, and in many other respects the st interesting, dinosaurian 



reptiles vet 1 1 i>co\ erei I ill ;I1IV pari of tile Wofhl. Tile Weils ;UV of \ er\ 



limited extent, so far as now known. They have not vet Keen detected in 

 the I >enver Basin. 



BAPTANODON BEDS. 



The Baptanodon \>f<\> placed next in the section have also no1 been 

 recognized near Denver, nor along the same horizon to the south, bul are 

 strongly developed in Utah and Wyoming on the flanks of the LTinta and 

 Wasatch mountains, ->n the Laramie Plains, in the Big Morn and Wind 

 River ranges, and al various other point- farther north. They consisl of 

 marine Btrata, inclosing many typical invertebrate fossils in addition to the 

 large reptile. Baptanodon, from which the horizon takes its name. As these 



