W. Cross — Post-Laramie Deposits of Colorado. 29 



section, the Jura, and the Archaean. This was clear in the 

 horizontal position of the " lignitic " strata of Mt. Bross which 

 rest upon upturned Dakota and Ft. Benton strata, and of the 

 ridge south of Hot Sulphur Springs. The relationships are 

 expressed in the Hayden atlas and in the large scale maps 

 accompanying Marvine's report, to which the reader must be 

 referred for details. The u thin seams of carbonaceous 

 material " mentioned by Marvine became coal beds in subse- 

 quent writings of other geologists, and the fossil plants said 

 to have been collected here were identified by the paleobotan- 

 ists as " Laramie," excepting a few which are described by 

 Lesquereux without explanatory comment as coming from the 

 Green River Eocene. The plainly provisional correlation of 

 these beds with the coal-measure horizon east of the moun- 

 tains by Marvine has not been questioned until recently. 



It is evident to any one intimately acquainted with the Lar- 

 amie proper that the description and statements of Marvine 

 do not establish a satisfactory correlation between the Middle 

 Park " lignitic " beds and the Laramie. In the light of the 

 investigations of the Denver region the unconformity noted 

 by Marvine and the thick beds of eruptive material at the base 

 of the series suggested a different correlation. In the summer 

 of 1889 Mr. George L. Cannon, Jr., of Denver, a geologist 

 well acquainted with the local formations, was sent into Mid- 

 dle Park by Mr. Emmons to examine the so-called " lignitic 

 formation " of Marvine. On the basis of Mr. Cannon's work 

 it has already been stated by Mr. Emmons that the Middle 

 Park series does not correspond with the true Laramie.* In 

 October, 1891, the writer visited Middle Park, extending the 

 observations of Mr. Cannon and determining still further the 

 relationships of the formation in question. A paper giving 

 the results of these examinations is in process of preparation, 

 but the main features may be here summarized. 



The statements of Marvine as to the unconformity existing 

 between the " lignitic " beds and the Cretaceous section are 

 very clearly correct. There are faults not noticed by him 

 which coni|)licate the local geology very much but they cannot 

 explain the transgression of the newer beds across the entire 

 Cretaceous section and to the Archaean. The unconformity is 

 also shown by an examination of the Cretaceous horizon upon 

 which the " doleritic breccia " rests in the section of the 

 " breccia spoon," the syncline above mentioned. It is evident 

 that no strata corresponding to the Laramie proper now exist 

 in this section. Marvine refers the strata below the " breccia " 

 to the Fox Hills, but gives no special reason for the assign- 



* Orographic Movements in the Rocky Mountains. Bull. G-. S. A., vol. i, p. 

 281, 1890. 



