64 ME. A. GEIKIE OK" THE AGE OF THE 



Ten years after the appearance of Macculloch's work, the Western 

 Islands were visited by two able observers, Yon Oeynhausen and 

 Yon Dechen, the latter of whom still survives as the universally 

 esteemed I^estor of German geology. In the careful description 

 which they gave of the portions of Skye visited by them we find no 

 trace of a suspicion that the limestone in the interior of Strath 

 ought not to be classed with the Lias. To quote their words; 

 ^' the connexion between the crystalline-granular limestone and the 

 ordinary Lias presents itself clearly before the eyes in so many 

 places that the former cannot be mistaken for a primary limestone, 

 which otherwise it most closely resembles " *. " The Lias is altered 

 to a granular limestone in the neighbourhood of the syenite" f. A 

 statement resting on the authority of the pioneer of Hebridean 

 geology and confirmed by such competent foreign geologists was 

 accepted as one of the established facts of the science. The altera- 

 tion of the Lias limestone of Skye into a white saccharoid marble by 

 the intrusion of syenite was thenceforth quoted in text-books as 

 one of the recognized examples of contact-metamorphism. 



Such was the state of opinion when, as a boy, I began my geolo- 

 gical career in the island of Skye. In exploring the geology of 

 Strath, I found it impossible to discover some of the sections described 

 by Macculloch, and I believed that he had mistaken the meaning of 

 others, but I accepted undoubtingly his view of the age of the 

 altered Kmestone X- ^ ^^^ years later, when again in Skye, tracing 

 the boundaries of the schists and older Palaeozoic rocks, I began to 

 suspect that some part of the Strath limestone could not possibly be 

 Lias, but must form an extension of the Lower Silurian belt which 

 runs from the north of Sutherland into the south-eastern part of 

 Skye. This suspicion was mentioned by me in a footnote to the 

 paper by Sir E.. I. Murchison and myself " On the Altered Eocks of 

 the Western Islands of Scotland " § ; but I was unable at that time 

 to investigate the subject further. Many busy years have since 

 passed away. It was not until two years ago that I found an 

 opportunity of returning to the examination of this interesting 

 question. Last summer I completed the mapping of the district, 

 and as I am now able to correct my original observations, I offer 

 the present communication to the Society, that the correction may 

 appear in the same Journal where these observations were published. 



I now propose to show that in Strath two totally distinct groups 

 of limestone have been confounded, one of them belonging to the 

 Lower Silurian system and a prolongation of the fossiliferous lime- 

 stones of Sutherland and Eoss, the other forming part of the Lias 

 of the Inner Hebrides, and to establish this distinction by the 

 clearest evidence, lithological, stratigraphical, and palaBontological. 



At the outset I would remark that the error into which geologists 

 have fallen in this matter was one which the structure of the 



* " Die Insel Skye," Karsten, Archly, i. (1829), p. 41. 

 t Ibid. p. 44. V /, 1- 



I Quart. Journ. Geol. Soc. xir. (1857), p. 1, 

 § Ibid. xTiii. (1861), p. 199. 



