REPORT OF ARCH. R. MARVmE, ASSISTANT GEOLOGIST DIRECT- 

 ING THE MIDDLE PARK DIVISION. 



WashijsGTON, D. C, June 19, 1874, 



Sir : 1 submit herewitli my report on the geology of tlie region trav- 

 ersed by the ISTorthern or Middle Park division of the United States 

 Geological and Geographical Survej^ of the Territories during the work- 

 ing season of 1873. 



The field was taken May 29 with a party proper consisting, beside my- 

 self, of Mr. G. E. Bechler, topographer ; Mr. S. B. Ladd, assistant topog- 

 rapher ', Sheppard Madeva and Eobert Mitchell, packers, and George 

 Bowline, cook ; the transportation of our baggage being effected by 

 means of a train of seven pack-mules. The methods of work were pre- 

 cisely the same as in the other parties. Messrs. Gardner, Holmes, and 

 Chittenden accompanied the party during the first month of the season, 

 when the base-line was measured, and the movements so directed that 

 the stations forming the first expansion of the primary triangulation 

 could be conveniently visited. When Mr. Gardner left to continue this 

 work, and Messrs. Chittenden and Holmes to join their respective par- 

 ties then entering the field, Messrs. Enos T. Luce and S. H. Nealy, gen- 

 eral assistants, joined me, and the work was directed solely to serve the 

 X^urposes of the detail topography and geology. The continental divide 

 over into the Middle Park was i)ermanently crossed on September 2, 

 soon after which Messrs. Luce and Nealy returned, reducing the party 

 to its original number. In mid-October the breaking up of the season 

 rendered it judicious to return over the mountains before permanently 

 closed with snow, and on the 15th of the month we turned homewarcl, 

 leaving a portion of the work in the vicinity of Breckinridge incom- 

 plete. Being on the route to our work of the coming season, it can 

 then be conveniently and speedily finished. 



The area actually examined during this interval of time, so that both 

 its topography and geology can be mapped in considerable detail, is 

 nearly four t'jousand square miles, which, by material obtained fi?om the 

 land-surveys upon the plains, has been extended eastward to include a 

 total area of over fifty-six hundred square miles. This area is approxi- 

 mately in the form of a rectangular belt sixty miles wide north and 

 south, the eastern end resting on the western border of the great plains 

 and including Denver City, and extending westward over the main chain 

 of the Eocky Mountains, and across the Middle Park to the Park range 

 bordering the latter on the west. West of the plains there are no large 

 level areas to facilitate rapidity of work, while much of the zone of 

 mountain country bordering the main divide on the east not only i)re- 

 sents peculiar difficulties to rapid and at the same time accurate map- 

 ping, but it is comparatively thickly vsettled, and demanded much more 

 time for its completion than equal areas elsewhere. Mr. Bechler's map 



