ALTERED LIMESTONE OP STRATH, 8KYE. 71 



island is in its original or undisplaced position, but that the whole 

 of them have been dislocated and driven bodily westward. 



(2) The Lias. — That the Silurian Limestone must be separated 

 from the Lias by a complete discordance is obvious from the struc- 

 ture above described, even if no visible un conform ability were trace- 

 able. But there is the most complete proof of a great physical break 

 between the two rocks. The base of the Lias along the western 

 margin of the belt which crosses Strath is formed of a conspicuous 

 breccia, consisting mainly of fragments of limestone, with pieces of 

 chert, quartzite, and red sandstone. In my early survey of Strath, 

 when the whole of the limestone was regarded as of Liassic age, I 

 naturally considered this limestone breccia to mark a local break in 

 the Secondary series of rocks. Its true meaning is now apparent. 

 The limestone fragments of which it mainly consists are not derived 

 from any part of the Lias, but from the Silurian series, and prove the 

 extensive denudation of that series in Liassic time. From Sithein, in 

 Strath Suardal, where it contains a large percentage of quartzite frag- 

 ments and lies between the areas of Cambrian sandstone and Silurian 

 limestone, it can be traced all round the margin of the red sandstone 

 area, dipping gently under the overlying Lias limestone and shales. 

 Only at one place have I found it visibly touching the older limestone ; 

 this is in the glen of the Allt Leth Slighe, or halfway burn, between 

 Kilbride and Suishnish Point, where the breccia attains its maximum 

 thickness — some 50 or 60 feet — and lies with a striking unconform- 

 ability upon the edges of the steeply inclined Silurian limestone. 

 The section, which is represented in fig. 2, completes the demonstra- 



Fig. 2. — Section in Allt Leth Slighe^ Strath. 



e. Blue, somewhat fetid limestones, full of broken shells (Lias), d. Limestone 

 breccia (50-60 feet) consisting mainly of fragments of the under- 

 lying limestones, with abundant pieces of chert and quartzite. 

 c. Granophyre ("Syenite") of Beinn an Dubhaich. b. White lime- 

 stone, a. Dark-grey limestone full of worm-casts and pieces of 

 chert. 



tion of the entire separation of the Liassic strata from the more mas- 

 sive or so-called " unstratified" limestone of Strath. 



Immediately to the west of this instructive section the breccia is 

 rapidly overlapped by higher Liassic beds, which rest directly on the 

 Silurian series. The boundary between the two groups of rock runs 

 down the glen, and in half a mile reaches the little ravine by which 

 the stream discharges itself into the sea. Thence the liae of sepa- 



