404 



At a depth of 48 feet, the shaft passed through a bed of shells 3^ feet 

 thick, with just clay enough to hold them loosely together. Two species 

 were identical with fossils previously found by me in the clay, over a 

 bed of coal, at Hallville, on the Union Pacific Railroad. That this bed 

 of shells is above the marine sediments, and in brackish deposits, is evi- 

 dent. ISTowhere has there been a strictly marine fossil discovered above 

 or very near the lowest seam of coal. 



About nine miles southeast of Cheyenne, there is a bed of coal, near 

 the base of the Lignitic group, just over which, is a bed of oyster-shells 

 three or four feet in thickness. The brackish character of the sediments 

 of the lower portion of the Lignitic group is universal from British 

 America, on the eastern slope of the Eocky Mountains, to is'ew Mexico 

 Near latitude 41°, a few miles south of the Union Pacific Railroad, on 

 the east base of the mountains, the Lignitic group passes beneath the 

 more modern White River group, and re-appears to the northward, about 

 the line of parallel 43°. By examining the two geological maps, which 

 I have long since published, the connection of the Colorado Lignitic 

 Avith that of the Xorthwest will be at once apparent. It is not necessary 

 to prolong these notes in this place, as the details of this subject have 

 already been i)ublished in previous reports or will be fully elaborated 

 hereafter. It re-mains now to deduce the following conclusions : — 



1st. So far as Eastern Colorado is concerned, extending from Raton 

 Hills to Cheyenne, we have no knowledge of any but brackish-water 

 deposits of the age of the Lignitic group. IsTot a species of exclusively 

 marine in vertebrata passes above the lowest bed of coal. The sea- weed 

 Halymenites is found in the Upper Fox Hills group and in the Lower 

 Lignitic, but no special importance can be attached to this form as a test 

 of the age of any group. 



2d. It is evident that in many localities, and possibly throughout 

 Eastern Colorado, a considerable portion of the Upper Fox Hills group 

 is wanting. Sometimes the Lignitic group is deposited on iSo. 4 or No. 

 3 Cretaceous. Therefore, there is undoubtedly a conformable interrupted 

 sequence; in other words, while the Lignitic group appears to conform 

 to the underlying beds, there really are wanting hundreds, and perhaps 

 thousands, of feet of strata which at some other locality in the West 

 may exist. 



3tl. The fact that not a single form of animal or vegetable remains of 

 strictly marine origiu passes above the well-marked Cretaceous or Fox 

 Hdls group into the Lignitic, shows clearly that there is here a most 

 important time-boundary ; that not only stratigraphically, but biologi- 

 cally, one great epoch ends and another commences, each of which is, in 

 every respect, distinct from the other. 



4th. Inasmuch as the evidence is clear that the animal and vegetable 

 forms below the base of the Lignitic group are strictly characteristic of 

 the Cretaceous epoch, while in the Lignitic above, the vegetable life, with 

 its great variety of forms, is regarded by our best authority, Professor 

 Lesquereux, as purely Tertiary, and inasmuch as not one characteristic 

 Cretaceous invertebrate has been found above the lowest bed of. coal, 

 but all have decided relations to Tertiary forms, we think we are war- 

 ranted in regarding the Lignitic group of Eastern Colorado as of Eocene 

 age. 



In regard to the great coal-deposits of the interior of the continent, I 

 desire to make some explanations in connection with the very valuable 

 paper of Professor Lesquereux, which precedes this. During the past 

 season, while endeavoring to gather materials to aid in settling the vexed 

 problem of the age of these coal-deposits, after having examined wiih 



