62 MR. A. GEIKIE ON THE AGE OE THE 



7. On the Age of the Altered Limestone of Steath, Skte. By 

 Aechibald Geikie, Esq., P.E.S., F.G.S. (Eead December 7, 1887.) 



The alteration of the Lias limestone of Skye into white marble by 

 the intrusion of masses of eruptive rock has been long regarded as 

 one of the most interesting features of that attractive island. The 

 first announcement of this metamorphism was made by MaccuUoch, 

 io a paper read by him before this Society in the beginning of the 

 year 1815. He there described the transition from ordinary un- 

 altered shelly Secondary limestone into an irregular shapeless 

 " marble limestone " in which all semblance of stratification had 

 been lost, and of which the general structure resembled that of the 

 Assynt limestone of Sutherland. He was at first inclined to regard 

 this massive rock as a " primary" limestone, which it had naturally 

 been supposed to be ; for he found it exactly to resemble the lime- 

 stones associated with schists and granites in various parts of the 

 Highlands. But he discovered what he considered to be a regular 

 alternation of the marble limestone and shell-Hmestone, which re- 

 moved " the last shadow of a doubt " from his mind as to the real 

 identity of the rocks. The obliteration of the stratification and the 

 assumption of a more crystalline texture he believed to be not 

 improbably due to the invasion of the limestone by eruptive masses 

 of " syenite " *. 



Pour years after the appearance of this memoir, MaccuUoch 

 gathered together his numerous observations on the geology of the 

 "West of Scotland, and published them in his classic work on the 

 "Western Islands. Among the sections of that book which arrested 

 the attention aud evoked the admiration of geologists, none has pro- 

 bably been more widely read and more frequently quoted than that 

 which describes the igneous rocks of Skye and their effects on the 

 adjacent strata. It contains a fuller description of the meta- 

 morphism of the Secondary limestone, but the statements of the 

 original paper remain essentially unchanged. The writer points out 

 that on both sides of the narrow part of Skye, Secondary limestones 

 and shales, crowded with well-preserved organic remains, can be 

 traced in regular succession for miles along the coast-line. In 

 lithological character and general sequence these strata were recog- 

 nized by him to be unquestionably parts of that great series of 

 Secondary formations which he was the first to trace out along the 

 western sea-board of Scotland. But though the coast-sections were 

 perfectly clear and intelligible, he stated, more emphatically than 

 in his earlier memoir, that this regularity and continuity entirely 

 disappeared in the interior of the island. Instead of weU-bedded 

 and gently inclined strata, he found limestones in which he said he 

 could detect no stratification, but which on the other hand had 

 acquired a crystalline structure more suggestive of some of the 

 * Trans. Geol. See. vol. iii. pp. 1-3 (1816). 



