272 S. P. EMMONS — OROGRAPHIC MOVEMENTS. 



ore-deposition of the region must also be assigned to a period anterior to 

 that movement.* 



North of the Gore mountains, the Park range opposite Middle park was 

 submerged, for a distance not yet determined, during the Jura-Dakota sub- 

 sidence: hut the northern part of the range remained above water, and the 

 Grand Encampment mountains may, as already suggested, have formed 

 pari of the Bame island with the Medicine Bow range. Tertiary and Recent 

 deposits now mask the ilanks of these mountain masses to such an extent 

 that all that can he said with certainty is that the Cretaceous deposits 

 wrapped around them without apparently extending up the present valley 

 of the North Platte as far a.- the North park. 



11'-/ Mountain and Sangre de Cristo Island*. — During or possibly even 

 before the Jurassic elevation, these two islands were consolidated into a .-ingle 

 land-mass, which may now be called the Sangre de Cristo island. If any 

 Triassic sediments had been deposited between them upon the upper Car- 

 boniferous they had been entirely eroded away. The eastern shore-line of 

 this land-mass had the .same general outline as the mountain front of tO-day, 

 with a reentering bay at Huerfano park extending somewhat further into 

 Wei Mountain valley than it does at present, and probably some submerged 

 ridges making out at an angle from this shoredine. Either from unequal 

 deposition over these ridges, as explained above, or on account of an unequal 

 erosion of the Triassic beds, the latter are only found at widely separated 

 intervals along the flanks of the Wet mountain range, and are apparently 

 altogether wanting along the Sangre de ( Jristo range, except possibly at its 

 southern end, in New Mexico. The Jura-Dakota beds consequently rest for 

 the most part upon upper Carboniferous or Archaean rock- at different 

 points along the shore line. 



The western limits of the Sangre de Cristo island may never be accurately 

 determined, for the reason that on this side tire basement rock- are now com- 

 pletely concealed beneath the recenl alluvial deposits of the San Luis valley 

 and the immense flowsof igneous rocks Lo the north and wesl of this de- 

 pression. From observed conditions in the present known exposures of 

 Mesozoic beds in this region, however, il seems probable that it formed a 

 continuous land-ma-- with the San Juan uplift, and that the dura- 1 >akota 

 ,-hoie line bent around the southern end of the present Sangre <le Cristo 



• to Bay tbat a local it) of critical importance with reference to this movement ha* 



not, i can learn, ever been visited by any geologist now living. This lathe northwest 



i mountains where the Mosquito fault, according to the Indications of the Hayden 



Map, aft* i eparating the Triass the wesl from the Archaean on the east, Is cut ofl .'it right an 



by Jura-Dakota bi ten Ins; acro»N Its path and resting on either formation. The iceologTcal 



outlines there given, however, were laid down by the hand "i Mr \ R Mai v Ine, who surveyed i in- 



lon.but whose untimely deatl u i written up his field notes i"r puhlfca- 



curacy of Mr. Marvlne's work that I have 



no hesitation in accepting I lal correctni lines, whioh are partially confiri I 



by tl ' Mr. Holi , who crossed the fault a few miles south of this point, and by 



elf and n ants, who lun- I minutel) tbe Mosquito fault northward to 



within twenty miles <•! this point. 



