Page:The Journal of geology (IA journalofgeology21894univers).pdf/42

Pittsboro, the only rocks seen were of the same general character. On the farm of Spencer Taylor, Esq., in Pittsboro, a bright red porphyry with flow lines is exposed in so altered a condition that it can be easily cut into any form with a knife, though it still preserves all the details of its structure. It looks not unlike the well known pipe-stone, or Catlinite of Minnesota. Three quarters of a mile beyond Pittsboro on the Bynum road there is a considerable exposure of a basic amygdaloid. South of Hackney's Cross Roads there are other excellent exposures of the ancient rhyolites with finely developed spherulitic and flow-structures. Numerous specimens were here collected which place the character of these rocks as surface flows beyond a doubt. Another locality in the volcanic belt was visited on Morgan's Run, about two miles south of Chapel Hill. Here are to be seen admirable exposures of volcanic flows and breccias with finer tuff deposits, which have been extensively sheared into slates by dynamic agency. Toward the east and north these rocks pass under the transgression of Newark sandstone. The accompanying sketch-map (Fig. 2) shows the relations of the above mentioned localities in Chatham and Orange counties, N. C. From still another locality at the cross-road near the northern boundary of Chatham county, fifteen miles southwest of Chapel Hill, Professor Holmes informs me specimens of undoubted volcanic rocks have recently been secured; he has also sent to me within the past month a suite of similar specimens from Pace's Bridge on Haw river, three miles above Bynum.

In his upper division of the Taconic System in North Carolina, Emmons describes numerous beds of "chert or hornstone" intercalated in the slates and sometimes forming isolated bosses, whose origin he is at a loss to account for. He says they are not metamorphic, but does not suggest for them an igneous origin.^[1] The hypothesis that these rocks may also be of volcanic origin is sustained by Emmons' description of "brecciated conglomerates" associated with the chert beds, which are composed