FATTNAL EVIDENCE AND COKRELATION. 265 



Kansas section, while the variety of Productiis mmireticulatus common in the Kansas 

 section is not found in Colorado at all except possibly at Sinbads Valley. Productus 

 injlatus, on the other hand, which is rather characteristic of the lower division of 

 the Hermosa formation, is extremely rare in the Kansas section. The same is 

 true of Pi'oductuJi gallatinensis. Spirifer rockymontantis and Spirifer hoonensis{?). 

 which, being- of the Keokuk group of spirifers, may be considered rather 

 Mississippian than Pennsylvanian types, though found abundantly in the Mis- 

 sissippi Valley at horizons I believe to be older than the Kansas section, 

 do not occur in the latter at all. The}^ are abundant in Colorado, and generallj^ 

 throughout the Rocky Mountains. Spiriferina campestria also, which is all but 

 identical with the Mississippian Spiriferina fpinosa, is not known in the Kansas 

 section. Considerable other evidence might be adduced, but enough has been 

 given to be significant. The evidence of the gasteropods and pelecypotls is less 

 clear, but in the main it bears out that of the brachiopods and Bryozoa, which have 

 just been hastilj'' referred to. However, as these tvpes are less common than the 

 brachiopods, their range is less completely known, and as they are more often poorly 

 preserved and more difficult to identify they are not as a rule as practicable for 

 evidence. A possible contradiction to the tendenc}' of the foregoing- evidence may 

 exist in Pseudomonotis Itmoni, a single doubtful instance of which is found in the 

 Hermosa formation, while in Kansas it seems not to come in until toward the- close 

 of the section. Other species of Pseudomonotis, however, appear earlier, as, for 

 instance, Pseudomonotis equisiriata, which is present in the lola limestone (16). It 

 seems to me, however, that there is abundant evidence to prove that the Hermosa 

 formation and its correlates (except the upper portion exposed in Siijbads Valley) 

 are not younger than the lower portion of the Kansas section, and that they probably 

 are somewhat older. I might add that I believe this to be true of a large part of the 

 Upper Carboniferous of the West, and that its more or less unfamiliar facies is often 

 due to its being older than the well-known faunas of the Upper Coal Measures of 

 the Mississippi Valley. 



Owing to the faunal break between the Hermosa and liico formations, and to 

 other evidence already several times refei-red to, I believe that sedimentation was 

 not continuous in the San Juan region from one period to the other. It will be 

 necessary, therefore, to discuss the age of the llico fauna independently. Several 

 yeai's ago, when I think it may be said that less was known of the sequence in Kansas 

 and Nebraska, 1 had occasion to consider this same question, and reached the 

 conclusion that the Rico period occurred late in the Kansas section, not so late as 

 the Marion formation, but about at the time of Prosser's Neosho and Chase, the 

 Permo-Carboniferous of Meek and Hayden, which he includes with the Marion to 

 constitute the " Permian " of the Mississippi Valley. My conclusions at that time 



