246 C. W. TOMLINSON 



flat-pebble conglomerate. Walcott 1 places the lower boundary of 

 the Upper Cambrian approximately in the middle of this lower 

 series (Member o), at the base of a sandstone member. No fossils 

 have been found in the 1,000 feet of beds (Nounan formation) next 

 beneath that horizon, but the Bloomington formation, next below, 

 carries a Middle Cambrian fauna. 2 As the shales of Member o in 

 Montana and Wyoming have been assigned to the Middle Cam- 

 brian, they are possibly to be correlated with the green shales of 

 the Bloomington formation. 



Members 3 and 4 in northern Utah. — The main flat- pebble con- 

 glomerate series (Member 3) on Blacksmith Fork is 800 feet thick, 

 and has yielded fossils at several horizons. These collections have 

 established the Ordovician age of all but the lower 190 feet of the 

 member, which is left by Walcott 3 in the Upper Cambrian. The 

 Garden City formation in the Randolph quadrangle is described 

 by Richardson 4 as containing flat-pebble conglomerate throughout 

 its estimated 1,000 feet of thickness, but it may include a repre- 

 sentative of Member 4 as well as of Member 3. Richardson's 

 collections 5 are like those of the writer from Member 4 on Black- 

 smith Fork, and clearly indicate that this formation is of Beekman- 

 town age, possibly ranging up into slightly later time. 



Richardson 6 states that he has evidence of an unconformity 

 between Cambrian and Ordovician, but this evidence is not yet 

 published. Elsewhere in Utah no evidence has been cited of an 

 interruption in sedimentation at this horizon, and it is certain, as 

 indicated by the exact similarity between the latest Cambrian and 

 the earliest Ordovician rocks, that if similar conditions were not 

 continuous from the former period into the latter in this region 

 they returned with very little modification after the interruption. 

 The upper record succeeds the lower without the intervention of 

 any clastic sediments. 



1 C. D. Walcott, "Cambrian Cordilleran Sections," Smithsonian Misc. Coll., LIII 

 (iqio), 193. 



a Walcott, op. cit., pp. 194-95. 3 Op. cit., p. 191. 



4 G. B. Richardson, "The Paleozoic Section in Northern Utah," Amer. Jour. Sci., 

 4 th Ser., XXXVI (1913), 406-15. 



5 Op. cit., pp. 408-9. 6 Op. cit., p. 408. 



