405 



as raach care as the time would i)ermit the line of jimctiou in Eastern 

 Colorado, 1 spent some days along the Union Pacific Railroad as far as 

 the station at Green Eiver. Having studied the geology of this portion 

 of the West from Cheyenne to Great Salt Lake more or less since ISGS, 

 I became convinced that the region where this problem is to be settled 

 lies in the interior of the West, in Western Wyoming and Eastern Utah, 

 and so stated in my annual report for 1873 * It is here that the conti- 

 nuity will be found to be more complete than in any other portion of 

 the West. 



In Bulletin ISTo. 2, first series, I gave a brief account of my investi- 

 gations of the Lignitic group and the reasons that led me to consider it 

 entirely of Tertiary age. Having explored it for over twenty years in 

 the Northwest, where it is nearly all of fresh- water origin, having traced 

 it with much care from latitude 49° southward to K"ew Mexico, through 

 nearly twelve degrees of latitude, and over an area of from one hundred 

 to one hundred and fifty thousand square miles, where the evidence, 

 either directly or indirectly, leaned to the Tertiary age of the group, I 

 was led to the opinion that it formed a separate group, which was 

 brackish-water at base and gradually passed up without interruption 

 info the beds of purely fresh-water origin. Wherever fossil plants were 

 discovered to any extent in its southern extension, species were identified 

 as the same with those so abundant on the Upper Missouri. During the 

 summer of 1868, I made a careful exploration of the coal-beds at Coal- 

 ville, Utah, and at Bear Eiver on the Union Pacific Eailroad, when I saw 

 for the first time the unmistakable proof that the coal-beds extended 

 down into the Cretaceous series. At Bear Eiver, near the west line of 

 AVyoming, there was an abundance of well-marked Cretaceous fossils 

 above and below the most important beds of coal. At Coalville, the 

 workable bed of coal seemed to l)e far down into the Cretaceous. In 

 the Proceedings of the American Philosophical Society at Philadelphia, 

 February 19, 1869, page 48, I published a brief account of my examina- 

 tions. 



As far back as 1853, 1 had known of the existence of a seam of coal 

 in the Dakota group, and from time to time traces have been found 

 even in the Fort Benton group above; but that coal-beds extended all 

 the way from the Jurassic through all the divisions of the Cretaceous, 

 up to the summit of the Lignitic group, was not known to me. The dis- 

 coveries of various geologists in the interior of the continent, especially 

 in New Mexico, Arizona, and Utah, show this to be the case. Mr. 

 Holmes and Dr. Endlich, assistant geologists with this survey, have 

 found in Southern and Southeastern Colorado, during the past season, 

 heavy beds of coal all through the Cretaceous groups from the base up. 

 These coal-beds were observed during the summer of 1874 by members 

 of the survey near the boundary -lines between Colorado, New Mexico, 

 and Arizona, with an abundance of Cretaceous fossils above and below 

 the coal-beds. 



In Bulletin No. 2, first series, dated April, 9, i 874, 1 made this statement: — 

 "As-we go southward into Southern Utah, New Mexico, and Arizona, the 

 greater portion of the coal-beds are in rocks of undoubted Cretaceous age. 

 It seems conclusive therefore that the Lignitic group began in the Creta- 

 ceous period in the marine seas, and continued on upward, through the 

 brackish-water times, into the purely fresh-water deposits." It is plain, 

 therefore, that much of the difference of opinion about these deposits 

 among field geologists is like the story of the shield. Those who have 

 worked from the south and southwest toward the north have been 



* See Annual Report for 1873, page 26. 



