274 S. I. EMMONS — OROGRAPHIC MOVEMENTS. 



the Jura-Dakota beds with those on which they rest are along the western 

 thinks of the mountains in the presenl valleys of Slate and East rivers, which 

 flow southeast, and of Rock creek, which flows northwest. A.long th 

 valleys the beds are now upturned at a sharp angle and often inverted, and 

 it is by discrepancy in strike alone that the unconformity is shown. Pro- 

 ding northwestward from the Gunnison river up the former valleys, the 

 Jura-Dakota beds are first found resting directly upon the Archaean : then 

 <>n tin- east side of the valley, neglecting minor irregularities due to local 

 folds and faults, they resl successively on upper Cambrian, Silurian, lower 

 Carboniferous, upper Carboniferous, and. finally, at Copper creek, opposite 

 the town of Gothic, mar the head of East river, they rot in apparent angular 

 conformity upon the Triassic"Red Beds." Following the strike further 

 northwestward, the Jura-Dakota contact descends again in horizon, resting 

 upon upper ( larboniferous beds and. around the remarkable Archaean protru- 

 sion of Treasury mountain, upon lower Palaeozoic Limestones, now changed to 

 most beautifully variegated marbles. Still further north along the valley of 

 Rock creek, the upper Carboniferous and Trias come successively up to the 

 base of the Jura-] Dakota. 



In the region along the Grand river and the White river plateau beyond 

 it. which has not been visited by the writer, no unconformity between the 

 Jura-Dakota and Trias is noted by the members of the Bayden survey, 

 though the outlines on their maps are such as to surest that evidence could 

 he found both of this and of the earlier movement if they were Studied to 

 this end. 



Western l!'<ii<>n. — [n the broad area south of the Gunnison and Grand 

 rivers, which was a region of comparatively little disturbance in pre-Creta- 

 lus time, no evidence of unconformity was noted by the members of the 

 Bayden survej who visited it. The beds which they classed as lower 

 Dakota in the coloring of their map are, however, the lithological corre- 

 spondents of the Atlanto8auru& beds a- developed in the Elk mountain region ; 

 and Mr. Bolmes ha- recently Btated to me that he now considers them to 



belong below the Dakota and to he probably of Jurassic age. 



< )n the eastern shore line, at the base of the San Juan mountains, there is 

 a heavy littoral conglomerate and an evident unconformity at the base of 

 the Jura-Dakota, which ha- been noted also by Mr. K. ( '. Bills.* Whether 

 the limestone, which h< places below this unconformity and above the red 

 sandstones containing vertebrate and plant remains of Triassic age, should 

 be considered to represent the marine Jura of the Wasatch and (Jinta 

 mountain- i- somewhat uncertain, as no organic remain- have yet been dis- 

 covered in it. 



1/ Newberry and Holm,- both failed to find any 



km. Jour. Set., 3d wr., Vol. XIX, June, i 



