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Show w I 39 and one packer to meander the main San Juan to its head, to make stations with gradients, to locate the heads of the stream and of the western branch of the Rio Piedra. Upon the completion of this, they were to gain the canon of the Rio Grande, and meandered the southern tributaries of that stream, which have their mouths between Antelope Park and the month of the south fork. This party, though experiencing very severe weather- the thermometer registering below zero- and much delay from the heavy snow upon the mountains, were successful in their efforts, and certainly deserve much credit for their resolution and self- sacrificing devotion to their work. My own party, after making twotriangnlation- stations with 10- inch theodolite upon the most prominent peaks in this portion of the continental divide, attempted to gain the Summit mining* district by way of the heads of the South Fork of the Rio Grande, but on account of the slippery and unsafe coudition of the steep sides of the canon of this stream from snow and sleet, we were compelled to abandon the attempt, aud to reach onr intended triangulation points near the head of the Alamosa, via Del Norte. Upon reaching this point, I purchased the necessary supplies and provisions and immediately sent Mr. Nell and party, via the Los Pinos Creek trail, to the Summit mining- district to occupy the triangulation- points which had been selected in that vicinity, with directions that he should, upon the completion of his monntain- work, carefully meander the Rio Grande del Norte from the town of Del Norte to the Costilla Ferry, thence proceed to Costilla, thence meandering the Costilla Creek to its head, make a barometric profile of the Costilla Pass and of the road via the Verm* jo Pass and the Purgatoire River to Trinidad. He was successful, in spite of snow, in closing, in a very satisfactory manner, our triangulation and in carrying out this programme. Mr. Atkinson having arrived at Del Norte, I started with him and one packer, meandered the road from Del Norte to Conejo-, thence to Fort Garland, thence to San Luis de Cnlebra, thence, via the head of the south fork of Culebra Creek, crossed over one of t h e highest points of the Spanish range to the bead of the main Vermejo, which stream we meandered as far as the Elizabethtown road, and thence proceeded to Trinidad, - where we arrived November 13, and where we found Mr. Nell and party engaged in selecting and marking out a base- line, to be measured by bim, and developed from the astronomical station at this point to the principal peaks in the Raton aud Spanish ranges, already occupied by other parties of the expedition. On the 15th of November, I detached the assistant topographer and a small party, and sent them to gather topographical details iu ihe drainage- areas of the middle and north forks of the Purgatoire River, to proceed to Pueblo for disbandment upon the completion of their work. A base- line nearly six miles in length having been located and marked, and all the necessary arrangements to aid in its measurements and development, for the erection of artificial stations, & c , having been made, I left Mr. Nell and party to complete this work, and proceeded, November 20, to Pueblo, for the purpose of supervising the disbandment of the several iield- parties of the expedition. The measurement of the baseline at Trinidad was completed by November 27, and t h e parties all disbanded at Pueblo, Colo., by December 2,1874. During the field- season, besides the executive charge of the party, I took the necessary sextant- observations for latitude at - points which could not well be located by triangulation- inethods; and when the party was divided, as was generally the ease, I carried the cistern- barometer, and took and recorded the barometric and psycbrometrio observations, for hypsometrical purposes, for the division I accompanied, all of which observations I haye since computed, and the results are in the hands of the topographers. INSTRUMENTS USED. The parties were well provided with instruments. The triangulation stations were occnpied with an 8- inch transit, made by Stackpole, reading by vernier to 10" of arc. Minor stations were occupied with a gradienter, reading to I7 of arc, and the meanders were executed with a Cassella theodolite, read-i? ff. hy vernier to 1' of arc; the distances being measured by odometer, and checked by sights to points well fixed bv triangulation. We carried two cistern- barometers, made by Green ; two 3- inch aneroids, with attached thermometers, made by Cassella, of London ; and two sets psyohrotneters for onr hypsometric work, together with the necessary appliances for refilling and replacing broken barometer- tubes. HYPSOMETRY. The observations required by the printed instructions, compiled and prepared by Lieut. R. L. Hoxie, Corps of Engineers, for the gnidance of members of the survey, were taken* These were, cistern- barometer and psychroiueter observations at camps and upon triangnlation and topographical stations, and aneroid and thermometer reudings a t all meander- stations. The system of observation, instrumental comparisons, field- transcripts, and records, devised by Lieutenant Hoxie, has worked admirably during the past season, and has been fruitful of the best results. Especially useful is the combination of the records |