106 GEOLOGICAL SURVEY OF THE TERRITOKIES. 



THE LIGNITIC FORMATION.* 



We turn now to tlie consideration of tlie group of rocks which lies 

 directly superimposed upon the Cretaceous beds, and which, economi- 

 cally considered, is of more importance than any of the preceding 

 formations. This is the formation that contains in its lower portions 

 the lignites of Eastern Colorado. To what epoch of geological time 

 this group of rocks should be referred, whether it should be considered 

 as an upward extension of the preceding cretaceous, or the commence- 

 ment of a more recent epoch, is a matter about which there is still di- 

 versity of opinion. Its fossil flora is very abundant, fifty-six species of 

 vegetable remains having been found at Golden City alone. Yet Pro- 

 fessor Lesquereux, the eminent authority in fossil botany, says that 

 throughout the group not a single leaf has as yet been found identical 

 with a Cretaceous species ;t and, further, that "no member of the 

 American lignitic, as far as this formation is known by its vegetable 

 remains, can be referred to the Cretaceous." | He concludes, from his 

 extended observations, " that the great lignitic group must be con- 

 sidered as a whole and well-characterized formation, limited at its base 

 by the fucoidal sandstone ; at its top by the conglomerate beds. That, 

 independent from the Cretaceous under it, and from the Miocene over it, 

 our lignitic formations represent the American Eocene." § 



There seem to be indications near the base of the group, however, of 

 Cretaceous fossils. Lesquereux, himself, calls attention to the fact 

 that Dr. Hayden and Dr. John L. LeConte have each found a badly- 

 preserved Inoceramus low down in the series. Both of these localities, 

 however, have since been carefully but unsuccessfully searched for fos- 

 sils ; while the similar occurrences which have thus far from time to 

 time been reported from various localities have, upon investigation, 

 been shown to be the result either of inaccurate observation, or that 

 the facts observed were wrongly interpreted, or their bearing over- 

 estimated, or else that they occurred at points where geological com- 

 plications of the rocks made all observation more or less uncertain, as, 

 for instance, at Golden City. Indeed, none of these observations so 

 far recorded can be considered as furnishing evidence in the case, and 

 should be thrown out. Only the occurrence of Cretaceous fossils bear- 

 ing the clearest and most undoubted relations to the adjoining beds, and 

 that at more than one or two exceptional localities, can, under the cir- 

 cumstances, be accepted as defining the age of this great overlying 

 formation. Even if further observations were to show that these occur- 

 rences were other than exceptional, or, perhaps, accidental, they would 

 not necessarily prove more than that these lower beds only were of Cre- 

 taceous age, or, as considered by Hayden, beds of transition between 

 the Cretaceous and the Eocene ; though, in view of Lesquereux's idea 

 of the definiteness of the formation as a whole, if the lower beds are 

 proved to be Cretaceous the rest of the series also could hardly, with 

 consistency, be considered otherwise. 



* So many facts have already been collected from this formatiou by observers of re- 

 pute tha,t, iu any attempt to give as complete an Idea as possible of the geology within 

 my specified area, it becomes necessary to draw upon these facts to a very great extent, 

 especially as the writer's opportunities for observation in these better-known upper beds 

 were quite limited. The endeavor will be made to make the material obtained from, 

 each authority supplement that from the others. The principal sources of information 

 have been the reports of James T. Hodge, Professors Lesquereux, F. V. Hayden, and 

 John L. LeConte, while much practical information has been personally given by Mr. E. 

 L. Berthoud, of Golden City, Colorado. 



tHayden's Report for 1872, p. 343. 



t Ibid, p. 419. 



§ Ibid, p. 350. 



