292 BROOKS AND KINDLE — PALEOZOIC ROCKS OB" UPPER YtfKON 



tors. It will be shown that a small fauna collected from the highest bed 

 in this Upper Carboniferous has certain affiliations with the j\Iesozoic, 

 which would go to show that the Carboniferous section of the Yukon is 

 complete from the Devonian to the Mesozoic. 



The lower of the two well defined formations, for which the name 

 '•'Calico Bluff" is proposed, embraces about 900 feet of black and gray 

 shales, with some slate and numerous interpolated thin beds of limestone. 

 The whole formation carries an abundant fauna, assigned to the Missis- 

 sippian by Dr George H. Girty, Its typical exposure is at Calico bluff, 

 on the Yukon, about 15 miles below Eagle (see map, figure 2). The 

 Calico Bluff formation is separated by an unconformity from the suc- 

 ceeding formation, here called the "jSTation Eiver." There can be little 

 doubt of this unconf ormal^le . relation, though no complete section was 

 found showing both. The relations are inferred from the apparently 

 abrupt change in character of sediments to fine limestone from coarse 

 fragmental material. It is not improbable, however, that detailed map- 

 ping may reveal a considerable thickness of strata lying between Calico 

 bluff and Nation river, as here described. Whether such strata, if found, 

 should be included in one or the other of these formations, or be mapped 

 as a distinct stratigraphic imit, must be left to the future to determine. 



As shown by the detailed section on a preceding page, the physical 

 changes involved in the transition from Devonian to Carboniferous sedi- 

 mentation embraced a continuation of the deposition of shale-producing 

 sediments interrupted at intervals by periods of limestone deposition. 

 The Carboniferous fauna seems to have made its first appearance in the 

 region with the advent of limestone-forming conditions, during the tem- 

 porary cessation of the deposition of black shale sediments. The regular 

 and frequent alternations of closely folded, light colored limestone and 

 dark shale, which characterize the Carboniferous portion of the nearly 

 vertical face of Calico bluff, give it an unusual and striking appearance, 

 as seen from the river (see plates 18 and 19). 



The Carboniferous fossils obtained here were submitted to Dr George 

 H. Girty, who reports the following species from bed 9; of the section 

 (see page 288), Avhich is the lowest bed holding Carboniferous fossils: 



Fossils from Bed 9j Calico Bluff 



Fenestella sp. 

 Polypora sp. 

 Cystodictya sp. 

 Stenopora ? sp. 

 Rhomiopora sp. 

 Derbya ? sp. 



Produetus aff. Mseriatus Hall. 



Productus sp. 



Spirifer aff. bisulcatiis Sowerby. 



Spirifer aff. keokuk Hall. 



Spirifer sp. 



Reticular ia aff. setigera Hall. 



