322 E. M. KiKDLE — heconnaissakce of porcupine valley 



cupine at New Eampart House. The creek section exposes here 1,000 

 feet or more of the quartzite series, which is uninterrupted by other beds. 

 The sharp contrast of the exposures of the intensely black slate-limestone 

 beds and the white quartzites is one of the most striking scenic features 

 of the Upper Eampart gorge near the boundary. Some dolomites also 

 occur in the quartzites, but they play a subordinate role as regards their 

 importance in making up the total mass of the series. 



Metamorphism is not very pronounced in this series, but the argilla- 

 ceous sediments are noticeably more altered than those of the higher 

 horizons. In the latter the shaly phase is found, as a rule, while in the 

 former the shales have been altered to slates or slaty-like slickensided 

 films where they are in very thin sheets interleaved with limestones, as 

 generally haf)pens. 



It is difficult to make any estimate of the thickness of these beds with- 

 out detailed work. The prevailing westerly dip, which continues for 

 about 6 miles below New Eampart House, points to a great thickness for 

 the series, but the possibility of faiilting and of close folding in a part of 

 the series leaves some uncertainty in regard to the actual thickness. Five 

 thousand feet would seem to be a conservative estimate, and it is probable 

 that a much greater thickness is represented. 



No fossils have been found in these rocks; consequently their age can 

 only be stated with reference to that of the oldest paleontologically deter- 

 mined beds of the section — the Ordovician. That they antedate the 

 Ordovician in age is indicated by the fact that no series corresponding to 

 them in lithologic features occurs in the portion of the geologic section 

 lying above the Ordovician. The several main divisions of the Paleozoic 

 section from the Ordovician to the Carboniferous have been recognized 

 on the Porcupine by their fossils. 



ORDOVICIAN LIMESTONE 



The Ordovician limestone is the earliest horizon w:hich has been recog- 

 nized by fossils. On the geologic map it has been practicable to distin- 

 guish the Ordovician and Silurian in only a portion of the area of their 

 occurrence. The Ordovician as well as the Silurian probably occurs in 

 the Upper Eamparts between the mouth of Eapid river and the western 

 border of the series just described. No fossils have been found, however, 

 in any of the horizons exposed along this portion of the river. Ordo- 

 vician rocks have been positively identified only in the Lower Eamparts, 

 where characteristic faimas were found at two localities. One of these 

 is at the lower entrance to the gorge. The second locality is some 3 miles 

 above the first. The Ordovician limestone is a hard bluish gray rock, 



