H. A. Nicholson — On the Lake District. 105 



district, is now in great measure dispersed, but the re-consideration 

 of the sections made at that time in traversing the district, suggest 

 the position assigned in this paper to the ferruginous Oolite and the 

 Collyweston slates. 



Some of these observations, which I now recall with so much 

 pleasure, were made in company with Captain L. L. B. Ibbetson, 

 F.G.S., Mr. J. Bentley, Mr. Samuel Sharp, F.S.A., F.G.S.,iM. 

 Triger, and the late Dr. Oppel, who has embodied part of his obser- 

 vations in his ffreat work on the Jura formation. 



III. — On the Eelations between the Skiddaw Slates and 

 THE Gkeen Slates and Pouphyhies op the Lake-district. 



By Henry Alletne Nicholson, D.Sc, M.B., F.G.S. 



THE Skiddaw Slates, or Lowest Silurian Eocks of the Lake- 

 district, are succeeded upwards by a great series of ashes with 

 interbedded traps and porphyries, to which the name of " Green 

 Slates and Porphyries " has been applied, and it has always been 

 believed that the relations between the two were those of perfect 

 conformity. As early, however, as the year 1867 I was led, from 

 certain phenomena which I had observed, to express the opinion 

 that " whether the Green Slates are really conformable with the 

 Skiddaw Slates is a question which admits of doubt, though data 

 are wanting to arrive at a definite conclusion." (Geology of Cum- 

 berland and Westmoreland, p. 33.) In the beginning of November, 

 1868, I discovered what seemed to be a marked want of conformity 

 between the Skiddaw Slates and the Green Slates, the localities 

 where this occurred being the eastern side of the mouth of the vale 

 of St. John, the west side of Derwentwater (near Lowdore), and the 

 mouth of Borrowdale. As these phenomena had not been previously 

 noticed by any former observer, and as they appeared to me to be of 

 considerable importance, I have made a systematic investigation of 

 the subject, and have arrived at the following results. 



Beginning with the main area of the Skiddaw Slates, in the 

 north-western portion of the Lake-district, the upward boundary of 

 the slates can be traced to the south of the area from Troutbeck on 

 the north-east to near Egremont on the north-west, a distance of 

 more than twenty-five miles. Along this line the relations between 

 the Skiddaw Slates and the overlying Green Slates are as follows : 



In the course of Troutbeck Beck, close to the little village of 

 Troutbeck, the upper, soft, and shaly beds of the Skiddaw Slates 

 are seen on the western side of the stream, dipping S.S.E. at 65°. 

 These are overlaid in the eastern bank of the river, by the basement 

 beds of the Green Slate Series, consisting here of cleaved felspathic 

 ashes, dipping S.S.E. at 50°. About three-quarters of a mile 

 further up the river the upper bed of the Skiddaw Slates are again 



^ It is interesting to record that Mr. Sharp has, during many years, collected 

 largely both in the neighbourhood of Stamford and Northampton from these beds, and 

 has thus enlarged our knowledge of the Oolitic fauna of thia district. 



