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Show RECONNAISSANCE IN THE UTE COUNTRY. 59 Considerable differences in results in damp weather were observable where the cross- wires were not made from the web of the " wood- spider," as was the case with these instruments when turned out by the manufacturer, the wires of wThich were of the web of tiie common house- spider, and would lengthen and " sag" when we meFwith humid weather on the Arkansas. One instrument ( the wires of which had been refilled with the web of the wood- spider) was much more trustworthy, and in this connection I think that it would be advisable to have the stadia-wires adjustable and not permanently fixed as these are, for in the event of an accidental breakage of wires the new wires could be easily adjusted to the rods, while had such an accident occurred on our expedition it would have been necessary to regraduate the rods, a tedious and inconvenient operation, in such a country, if done permanently, and liable to change if done with colored chalks. An important consideration is to keep down the weight of the instrument, which has to be carried on theshoulderon mule or horseback over difficultand often dangerous trails, and through miry forests, in which Government mules develop a penchant for crushing their riders' legs against tree- trunks. At these times the instruments must be handled easily to prevent their being broken. If it is possible, I think an instrument made of aluminum or aluminum-bronze would best meet the requirements of this service. Mr. Hamilton, a member of the firm of T. H. Whally & Co., instrument- makers, of New York, who have the repairing of the Government instruments at Willet's Point, described a French instrument captured from the rebels during the war and sent to them for repair, which, if it at all answers to the description given, would be invaluable for filling in details of these topographical surveys. As I understand, the instrument simply described is a telescope properly mounted, having its object- glass halved, the halves being of different focal length; when pointed to a distant object each half of the object- glass is so adjusted that the object is clearly seen through it, when the distance of the object is read off in meters on a scale attached. APPENDIX B. Geological observations made between Pueblo and Fort Garland, Colorado Territory.- Pueblo is situated in the valley of the Arkansas Eiver, on the margin of the great plains of the West. The vicinity is underlaid by a deep formation of drift, beds of slate, shale, marl, and gray limestone. The bluffs of the river are low, have a common level, and indicate an ancient shore- line. The route to Saint Charles lies over undulating prairie with the plains on the left. On reaching the Saint Charles Eiver the underlying rocks were found to be of an ashy- gray impure limestone, alternating with thin strata of shale or marl. In the bluffs is an exposure of ninety feet of these formations, extending down to the water of the river. The upper strata would make building- material for ordinary structures and fencing; they contain a few Inoceramus problematicus, Ostrea con-gesta, and some small species too obscure for identification 5 and many fragments of what appear to have been a large Inoceramus. The valley of Saint Charles is about \ mile in width, and the stream too inconsiderable to be called a river. The soil on the Mesa, between Pueblo and Saint Charles, is sandy, of a light- brown color and at some places contains an excess of the mineral salts. A good growth of Helianthus, remains of last year's crop,, indicate a good productive capacity when well watered. |
