Eleventh annual report of the United States Geological and Geographical Survey of the Territories : embracing Idaho and Wyoming : being a report of progress of the exploration for the year 1877 . haracter of some of these veins in that portion of therange at least. Besides these, there are a few dike-like exhibitions ofdark trap-rock, which at some points Professor Bradley found conform-able to the bedding of the granites, though it was difficult to decidewhether their occurrence in this position should be taken as indicatingtheir intrusive character, or were deposited as flows on the ancient
Eleventh annual report of the United States Geological and Geographical Survey of the Territories : embracing Idaho and Wyoming : being a report of progress of the exploration for the year 1877 . haracter of some of these veins in that portion of therange at least. Besides these, there are a few dike-like exhibitions ofdark trap-rock, which at some points Professor Bradley found conform-able to the bedding of the granites, though it was difficult to decidewhether their occurrence in this position should be taken as indicatingtheir intrusive character, or were deposited as flows on the ancient sur-face upon which the inclosing sediments were accumulated. One of thesetrap-dikes forms a well-marked feature in the southern base-of the greatcone of Mount Hayden, which may be traced as a dark ribbon descend-ing the west face and crossing intervening spur-ridges to the west, whereit is lost beneath the quartzite of the Potsdam, which crowns the ridgesin the neighborhood of the Pulpit. A very similar dike, doubtless also trap, occurs in the northern halfof Mount Moran, and which may be seen from either side, appearing like J>lc**& XXKJI. iV. nth of^Carboniferous^test U. *.! $iirvety. J>l&t& XJXJI. Wi .??;£,;
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