198 A. J. TIEJE 



to be of much the same age as the Fountain formation, a late 

 Paleozoic Front Range axis must have been continually rising in 

 order to supply such a thickness of sediments. The induction is 

 not out of accord with the present-day belief that the land mass of 

 "Columbia" underwent marked elevation in late Mississippian 

 time, nor with the view of Spurr^ and others that rejuvenation of 

 Colorado land masses occurred in early Pennsylvanian time. 



It is here desired, however, to suggest another possibility — 

 though by no means to cling to it. The thickness of the Fountain 

 formation increases, in general, from Cache la Poudre River to 

 Colorado Springs and then again decreases. It will also be recalled 

 that in the Colorado Springs section Lingulodiscina occurs 475 feet 

 above the base. Once, at least, there must have been an embay- 

 ment here. It may be that, although the main axis of the late 

 Paleozoic Front Range ran north-south, east-west spurs occurred 

 north and south of Colorado Springs, these spurs acting as divides 

 to rivers flowing northeast and southeast over whatever foreland 

 stretched in their courses. Limestone pebbles in the Fountain near 

 Boulder could not now be derived from the immediate west, and 

 at Badito are found the largest bowlders (much larger than those at 

 Colorado Springs) in the Fountain sediments. Only further and 

 very detailed studies^ can throw more light on the paleogeography 

 of Fountain times, but at least such evidence as is attainable 

 strengthens the river h5rpothesis. 



THE LYONS FORMATION 



Description: typical Lyons. — The t)rpical Lyons sediments, 

 though having the same strike and dip as the Fountain beds, have 

 not quite the same distribution, and are not easily recognized 



' J. E. Spurr, "Geology of the Aspen Mining Region," U.S. Geol. Surv. Monograph 

 31, P- 32. 



^ The Glen Eyrie shale, found only at Colorado Springs, needs closer attention. 

 G. I. Finlay, "The Glen Eyrie Formation," Jour, of Geol., Vol. XV (1907), p. 589, 

 suggests that the Glen Eyrie shale lies unconformably beneath the "purplish-red 

 sandstone," with "intercalated gray or light-pink arkose" with which the Fountain 

 begins. The Glen Eyrie shale, however, is also of Pennsylvanian age, and its Lepido- 

 dendron flora implies swampy lowlands. The facts strengthen the suggestion that 

 the Colorado Springs region at first marked an axis of depression rather than of 

 elevation. 



