492 JUNIUS HENDERSON 



to be stratigraphically continuous with the Fountain formation in the 

 Boulder District as defined by Dr. Fenneman/ who correlates it with 

 the Fountain of the Colorado Springs region. We have traced the 

 formation in the field the entire distance from the Wyoming line to 

 Boulder and find no reason to doubt that the horizon containing 

 the chert fossils is the equivalent of the base of the Fountain as repre- 

 sented at Boulder, or possibly even much higher than the base as it 

 occurs immediately north of Boulder, where the formation is much 

 thicker than near the Wyoming line. 



In limestones at a much higher horizon we found a Pennsylvanian 

 fauna (tentatively considered older than Knight's so-called "Permian" 

 of Wyoming), consisting of Productus cora D'Orb., P. nebrascensis 

 Owen, Spirifer rockymontana Marcou, Squamularia perplexa McCh., 

 Derbya n. sp. ?, Phillipsia aff. major Shumard, Myalina swallowi 

 McCh., abundant crinoid stems and others. These limestones were 

 said by Darton^ to pass into the Fountain conglomerates in traveling 

 southward. Of this we are by no means certain without further 

 investigation, but they seem certainly to belong at the very top of 

 the Fountain or base of the overlying Lyons formation of Fenneman's 

 bulletin. These limestones nearly disappear at the Cache la Poudre, 

 and a little work just north of that stream is necessary to determine 

 their exact position. We have traced the contact of the Fountain 

 and Lyons all the way from the northern line of the state to Boulder 

 except two or three miles between the Cache la Poudre and Owl 

 Canyon, and believe the Ten Sleep sandstone of Darton's paper to be 

 the stratigraphic equivalent of Fenneman's Lyons. 



It seems very clear that all of the Fountain sandstones and con- 

 glomerates of northern Colorado are Carboniferous, the base being 

 probably Mississippian (certainly so in the northern portion of the 

 field) and the upper portion possibly as late as Pennsylvanian. It 

 also seems likely that the Lyons is Pennsylvanian. 



The fossils were, through the kindness of Dr. T. W. Stanton, of the 

 United States Geological Survey, submitted to Dr. G. H. Girty, whose 

 determinations are followed in this paper. 



I N. M. Fenneman, Geology of the Boulder District, Colorado, U. S. Geol. Sur., 

 Bull. No. 265, 1905. 



» N. H. Darton, Geology and Underground Water Resources of the Central Great 

 Plains, U. S. Geol. Sur., Professional Paper No. 32, 1905. 



