1866.] 



J, GEIKIE — CARRICK, AYRSHIRE. 



513 



The metamorpliic rocks upon wMcli these beds repose have already- 

 been referred to as the equivalents of the upper quartz-rocks, upper 

 limestones, and upper gneiss of the Highlands of Scotland. As the 

 position of these metamorphic rocks in the sedimentary series is now 

 known in consequence of the fossils which the Lower Limestone at 

 Durness has afforded, and as the position of this limestone is not lower 

 than the Llandeilo flags, we must refer the metamorphic action which 

 has changed the purely sedimentary rocks to an age later than the 

 Lower Silurian period. 



Above the representatives of the Llandeilo flags there is, in the 

 Highlands of Scotland, a great thickness of quartz-rocks, lime- 

 stones, and gneissose strata; and the upper portion of this thick 

 series, in the form of the gneissose strata, very probably repre- 

 sents the Caradoc rocks. If this be the case, it follows that the 

 metamorphic action came into operation towards the close of the 

 Caradoc age. That the metamorphism of the gneissose rocks and 

 their associated strata was complete before the deposition of the 

 Upper Llandovery beds is proved by the occurrence, in the lower 

 portion of the fossiliferous Silurian rocks of Galway, of conglomerates 

 full of metamorphic fragments. All the circumstances which bear 

 evidence as to the period when metamorphism took place among the 

 altered rocks of this part of Ireland place this period in the Lower 

 Llandovery epoch. If this inference be correct, it must be extended 

 beyond the western portion of the county of Galway ; for it will em- 

 brace not only the whole of the metamorphic rocks of Ireland, but 

 also all those of the Highlands of Scotland, except the Funda- 

 mental or Laurentian gneiss. 



2. On tJie Metamorphic Lower Siliteian Eocks of Carrick, Ayr- 

 shire. By James Geikie, Esq., of the Geological Survey of Great 

 Britain. 



(Communicated by Professor A. C. Eamsay, LL.D., F.E.S., V.P.G-.S.) 



Contents. 



I. Introduction. 

 II. Felspathic rocks. 

 A. Amygdaloid. 



Succession of changes : — 

 1 a. Unaltered strata. 

 1 b. Slightly altered strata: ori- 

 ginal character quite apparent ; 

 bedding distinct. 



2. Granular strata with spora- 

 dic vesicular and amygdaloidal 

 areas: bedding distinct. 



3. Amorphous green paste -rock 

 with pseudo - bombs : bedding 

 lost. 



4. Felspathic amygdaloid. 



B. Felspar-porphyry. 

 Eecapitulation and statement of 



inferences. 



C. Brecciiform rocks. 



D. Finely crystalline felstones. 



III. Dioritic rocks. 



IV. Serpentine. 



1. Schistose serpentine. 



2. Compact serpentine. 



3. Association of diorite and ser- 

 pentine. 



V. Limestone. 



Association of serpentine with 

 calcareous strata. 



VI. Conclusion. 



I. Introdtjctioijt. 

 The metamorphic region which forms the subject of this commu- 



