174 REPORT UNITED STATES GEOLOGICAL SURVEY. 
me 
employed to represent the distribution of those post-Jurassic formations 
occupying the positions of the Cretaceous and Laramie formations in 
the geologic scale. In the latter instances, although the occurrences 
were visited, the evidence of their age in the majority of cases depends 
entirely on sequence or their stratigraphic position in reference to well- 
determined earlier formations in their neighborhood; the organic re- 
mains which these horizons afforded unfortunately were in so indifferent 
state of preservation as not to be recognizable with that degree of cer- 
tainty desirable in defining the age of the deposits whence “they came. 
It was therefore deemed “adv isable not to attempt the definition of 
Cretaceous and Laramie formations on grounds purely lithological, and 
this, too, in a region where apparently there exists no unconformity be- 
tween the various members of the great Mesozoic series; and hence the 
areas alluded to are given a single color with, however, queries and other 
legendary signs in accord with the impr essions arrived at as to the 
probable stratigraphical relations of the deposits therein met with. The 
familiarity acquired during a season’s hasty examination of large terri- 
tories, if it could be supplemented by revisiting special localities, would 
result in exact knowledge such as it may not be possible to arrive at in 
any other manner. As “it is, the work recorded on this map. materially 
amplifies that of earlier explorations in this region, the differences and. 
corrections being such as might be expected from the somewhat better 
facilities accorded the parties of this survey. 
It is with pleasure and a due sense of my indebtedness I here acknowl- 
edge the favors I have received at the hands of Dr. White, who, in my 
absence, kindly examined my paleontological collections whose deter- 
minations have given me greatest aids in preparing my report. Also to 
Dr. Peale and Professor Lesquereux I am uifler many obligations for 
the favor of important information. 
Very respectfully, your obedient servant, 
ORESTES ST. JOHN. 
Dr. F. V. HAYDEN, 
United States Geologist, in charge. 
