DEVONIAN 279 



Devonian limestones were found at intervals along the river between 

 the mouth of Coal creek and for some 3 miles below the mouth of Wood- 

 chopper. This limestone occurs interlarded among large masses of green- 

 stone, which latter must also find place in the Devonian. 



An entirely distinct belt of rocks, here also provisionally assigned to 

 tlie Devonian, is exposed in a series of cliffs skirting the south bank of 

 the river some 8 miles below Woodchopper creek. This belt includes 

 massive limestones, tliin-bedded limestones, shales, slates, and quartzitc^, 

 with a little tuff. Mesozoic beds cut off this series from another belt of 

 Devonian rocks, made wp chiefly of greenstones, with some slate and chert, 

 which continues to outcrop down the river nearly to Circle. 



The shales of the Eagle belt and the limestones of the Washington 

 Creek belts, as well as those interlarded with the greenstones at Wood- 

 chopper creek, carry fossils assigned to the Middle or Upper Devonian. 

 The limestone and slate series outcropping 8 miles below Woodchopper 

 creek yielded only a few fragmental fossils which have been assigned to 

 the Devonian. On general stratigraphic grounds the latter series is con- 

 sidered the oldest, and it is not impossible that it may be in part, at least, 

 Silurian. 



This last group, here considered, the oldest Devonian rocks, though it 

 may be of Silurian age, is exposed in a series of bold bluffs which mark 

 the southwestern bank of the river for a distance of 3 to 4 miles. The 

 strikes are about east and west and at right angles to the course of the 

 river. Close folding, shearing, and faulting have obscured the structure, 

 and the dips are varied, but most often to the north at angles varying 

 from 45 to 60 degrees. 



At the southern end of the section is a group of rock pinnacles made 

 up for the most part of a massive bh;e to white, semicrystalline, exceed- 

 ingly cherty limestone. Some shales occur with the limestones and some 

 of the limestone layers are so siliceous as to be better described as cherts. 

 This limestone has been much sheared and altered and all traces of bed- 

 ding obliterated, and it was impossible to determine the thickness, which 

 probably does not exceed a few Inmdred feet. In general it seems to 

 strike about east and west, parallel to the rest of the series. Diligent 

 search was rewarded by the finding of only a iew fragmental fossils, in- 

 cluding Favositcs sp. and Atrypa refiniJaris, and it is on the basis of these 

 indecisive fossils that the entire succession is provisionally referred to 

 the Devonian. To the north of the limestone, and probably stratigraph- 

 ically above it, is a mass of black sliale and chert, and then an anticlinal 

 fold appears to bring up the same limestone again. North of this fold 

 there is a monotonous repetition of dark flaggy limestones, green clay 



