656 MR. J. E. MAPvR AIS^D DR. H. A. NICHOLSON 



Stockdale Shales to the beds above and below. Against this ad- 

 vantage must be placed the paucity of sections, but especially the 

 constant occurrence of a strike-fault, which frequently cuts out a 

 great part of the series, and, as we shall eventually show, in every 

 case causes a portion to be missing. Nevertheless the number of 

 exposures is sufficient to allow us to piece together the whole of 

 the succession, save, possibly, at one point only, where we shall 

 give reasons for believing that if any portion of the deposit is now 

 entirely unseen in this district, it is only a very insignificant one. 



We would record our debt of gratitude to Professor Lap worth for 

 invaluable assistance, and to Professor Hughes for information 

 about the rocks of the Sedbergh district. 



§ II. I^OTICE OP Previous Writings. 



The first attempt at a subdivision of the rocks of the Lake-dis- 

 trict was made by Mr. Jonathan Otley, whose paper appeared ori- 

 ginally in the ' Lonsdale Magazine,' vol. i. p. 433, and subsequently 

 in the 'Philosophical Magazine' for 1820 (Phil. Mag. vol. Ivi. 

 p. 257). Mr, Otley adopted that threefold subdivision of the slates 

 of this area which was afterward supported by Professor Sedgwick, 

 and which forms the basis of all subsequent classifications. The 

 well-known narrow band of Coniston Limestone was shown to form 

 a natural separation between the slates of the second and third divi- 

 sions. This Coniston-Limestone band was proved by Sedgwick to 

 contain a fauna similar to that of his Bala rocks of J^orth Wales, 

 whilst the true slates of the third division undoubtedly contained, 

 in their higher portions, fossils similar to those of the typical Silu- 

 rian rocks of the area explored by Sir Eoderick Murchison. At 

 this time the beds which form the subject of this communication 

 were not separated oS from that division of the Upper Slates to 

 which Prof. Sedgwick, in 1845, applied the term " Coniston Flags ; " 

 so that aU that was written previous to the period when that sepa- 

 ration was effected, concerning the relationship of the Coniston 

 Flags to the Coniston-Limestone series, applies also to the relation- 

 ship between the latter and the Stockdale Shales. In Professor 

 Sedgwick's writings we find the Coniston Flagstones or Flags at one 

 time connected with the Coniston-Limestone series, at another 

 separated from these and miited to the rocks above them ; and he 

 finally adopts this arrangement, and, to quote the words used in his 

 ' Letters ' to Wordsworth, places the Coniston Flags " at the base 

 of the Upper Silurian series of the Lake District." 



The beds now known as the Stockdale Shales were origiually 

 distinguished by Professors Harkness and Nicholson in the year 

 1868, in a paper " On the Coniston Group " (Quart. Journ. Geol. Soc. 

 vol. xxiv. p. 296). 



These authors describe the lower portion of the Stockdale Shales 

 under the name of " Graptolitiferous Mudstones," and give a list of 

 fossils found in these beds at Skelgill and in Long Sleddale. They 

 refer to the beds now included in the upper part of the Stock- 



