sT.Joim] SECTION NEAR STATION XVII. 355 



8. Forty yards above tlie last, a similar hidden exposure of liglit gTay 

 limestone occurs, in Avliich were found a few small gasteropods. 



9. Drab argillo-calcareous indurated layers, apparently forming a 

 liea-\^ deposit in the crest of the ridge. Tliis ledge has evidently under- 

 gone much metamorphism from contact witli the igneous mass, by which 

 it is so changed and intersected by a bewildering set of cleavage as 

 quite to obliterate the bedding of the roclc. However, at several places 

 along the northeast side of the ig-neous dike it was possible to dis- 

 tinguish the planes of deposition from those of the superadded cleavage, 

 showing an inclination N. N. E., at a steep angle; and at a point nearer 

 the summit, the same ledges, here even more highly changed into an 

 exceedingly brittle, slaty rock, were found to dip in the same dii'ection 

 at angles of 30^ to 40°. 



10. This is a beautiful variety of hornblendic trachjiie, in which the 

 dark needles of hornblende are very generally disseminated, only sliow- 

 ing perceptible changes in the size of the crystals, which are embedded 

 in a dark gray matrix. The ledge stands up in a dike-like mass, with 

 a strike about E. 50° S. and W. 50° 1^., and apparently inclined seeply 

 to the southwest. It forms the highest part of the crest of the ridge for 

 the distance of about a mile, and several jards across. In the south- 

 west face, under Station XVII^ it presents a precipice in which the rock 

 is seen to be much broken by irregular joint structure. Farther north, 

 where the dike becomes less prominent, its outcrops is marked by debris, 

 which strews the surface with fine gravel, imi)arting to the soil a rusty 

 reddish color, markedly in contrast with the fine, Mght soil derived from 

 the decomiDosition of the calcareo-argillaceous deposits of the adjacent 

 slopes. 



11. Drab, indiu'ated argillo-calcareous deposits, interlaminated with 

 light gTay limestone layers containing great numbers of a small gaster- 

 opod. This horizon appears in the southwest slope of the crest, and is 

 much metamorphosed on api)roaching the igneous dike. 



12. Brown, partially fissile shales, with small concretions included in 



13. Drab, indurated, argillo-calcareous deposits, with thin interlamiua- 

 .tions of calcite. 



14. Eeddish gray sandstone, with slickenside surfaces. This ledge 

 outcrops in the bed of the little valley a short distance below, or to the 

 northwest of the line of the section, where it shows an inchnation south- 

 ward at an angle of 30°. Although a limitetl exposure, it is believed to 

 be the equivalent of one of the beds in the northeast flank of the ridge, 

 /probably No. 4, which it closely resembles lithologically. 



15. Obscure exposure of red shales. 



IG. Drab, indurated, fragmentary, argillo-calcareous deposits, with 

 seams of calcite and gypsum, api^arently forming a heavy bed, but im- 

 perfectly exposed in the northeast sloiie of low outlying ridge west of 

 Station XVII. 



17. Gray, fragmentary spar-seamed limestone, with numerous small 

 undetermined gasteropods. A thick stratum, defining an abrupt break 

 in the hill-side. 



18. In the gentle slopes of the before-mentioned outlying hill west of 

 Station XVII, a series of obscurely-exposed beds is met with, consisting 

 of alternations of gray and drab fragmentary limestone and heavier beds 

 of reddish and buff sandstones and softer deposits, which compose the 

 bidk of this lesser ridge. 



19. Basalt, fiUing the vaUey of the West Fork of John Day's Greet 

 and lapping ui^ on the sedimentaries all along the southwest flank of this 

 low highland ridge. 



