RECAPITULATION OF PALEOZOIC FORMATIONS. 155 



west of Trinidad — leaves little room for doubt that they are absent at that locality. 

 West of Canyon, in the northern end of the Sangre de Cristo Range, Silurian strata 

 occui', and are so colored upon the Hayden maps, as has already been remarked. 



On the western flank of the range, though no Silurian beds are mapped by the 

 Hayden survey, thej' have been recognized at one locality, at least, though the identi- 

 fication rests upon stratigrajjliic and lithologic, and not upon paleontologic evidence. 

 The locality is northeast of the town of San Luis, nearly opposite the point at which 

 Lee's section shows its absence on the east side. Lithologicallv, the Silurian here 

 appears to belong to the Yule limestone. 



Attention has already been directed to the difference between the Silurian section 

 of the Front Range and that of the interior of the State. The evidence is not at 

 hand to determine the relationship existing between the two sets of beds. If any 

 exact lithologic correlation is possible, it rests between the Yule limestone on the 

 one hand and the Manitou or Fremont limestone on the other. I rather expect that 

 the correlation will be made, if at all, between the Yule and Fremont. Emmons 

 correlated the Cambrian sandstone and Manitou limestone of Manitou Park with the 

 Sawatch quartzite and Yule limestone of the Leadville section (Leadville monograph, 

 p. 64). There deserves to be considei'ed in this connection the occurrence of the fish- 

 bearing horizons in the Paleozoic rocks of Colorado, these vertebrate remains being 

 in every case of the Devonian type. They constitute an important factor in the fauna 

 of the Harding sandstone and are found also in the Parting quartzite at Aspen, in 

 the middle or calcareous division of the Yule limestone at Crested Butte, and in the 

 middle or shalj' member of Cross and Spencer's Devonian in the San Juan region. 

 The latter I believe can with great probabilitj^ be placed in the Parting quartzite 

 horizon, and the other occurrences carrj^ the suggestion that possibl}' this formation 

 is the equivalent of the Harding sandstone. The sequence of the Sawatch, Yule, and 

 Parting formations is, therefore, suggestive of the Cambrian, Manitou, and Harding 

 beds of the Front Range. In this case the Yule would be correlated with the Manitou, 

 as Emmons has suggested, nor does the occurrence of these fish remains at Crested 

 Butte in the formation underlying seem to me a serious objection to this correlation. 

 On the other hand, Eldridge has suggested in the Anthracite-Crested Butte folio a 

 correlation of the middle or calcareous member of the Yule formation in which fish 

 scales occur, with the fish-bed in the Ordovician at Canyon. Cross relates that the 

 Fremont limestone is especially characterized by the occurrence of TIaly sites catenu- 

 latus, a fossil which is not rare in the Yule limestone. It should further be borne 

 in mind that the lowest division of the typical Yule is a quartzite formation appar- 

 ently assigned to the Ordovician on paleontologic evidence, and that in the Front 

 Range an unconformity intervenes between the Harding and Manitou beds. There 

 is thus considerable evidence favorable to correlating the lower and middle divisions 



