228 MESSES. B. N. PEACH Al^B W. GUNN ON [May I9OI, 



and ]Mr. Gunn found a small suite of fossils, which from examina- 

 tion in the field seemed to them to indicate the Liassic age of the 

 patch — a correlation subsequently confirmed by Mr. Newton. 



About 200 yards farther down £allymichael Glen from the above 

 locality Mr. Peach and Mr. Gunn noted blocks of limestone with 

 nodules of flint or chert, in which they detected foraminifera and 

 other organisms. The character of the rock, together with the 

 organisms, suggested the i^robability of the masses having been 

 derived from Cretaceous rocks in the condition of those now found 

 in Antrim. A large mass of similar limestone and chert, associated 

 with sandstone and shale, forms a cave (Pigeon Cave) situated 

 1100 yards north-east of Dereneneach, where it is underlain by 

 agglomerate and overlain by a basic igneous rock. Although the 

 limestone and chert are much altered, organisms were detected in 

 them by Mr. Peach and Mr. Gunn, and subsequently by Sir Archibald 

 Geikie, who, when inspecting the ground with Mr. Gunn, made 

 a collection from this spot. 



Another example of a limestone-mass, associated with sandstone 

 and shale, caught up in igneous rock occurs on the hillside, 550 

 yards south of the farm-house of Glenloig, where it was formerly 

 quarried for lime. The rock is free from chert, but too much 

 metamorphosed to preserve recognizable organisms. 



Other patches of sandstone and shale, believed to be of Mesozoic 

 age, occur either embedded in the agglomerate or caught up in 

 intrusive rock, but as yet they have yielded no fossils. 



So far as has been observed during the detailed mapping of the 

 ground, the intrusive igneous rocks are later in date than the 

 agglomerate. While in composition they range from basic to highly 

 acid material, in structure they pass from felsitic to granitic rocks, 

 and there is further a distinct petrological sequence in the intrusions, 

 the more acid rocks cutting the more basic. 



From the foregoing summary of the evidence relating to the 

 volcanic vent of Ard Bheinn the following conclusions may be 

 drawn : — 



(1) The great development of conglomerate, sandstones, shales, 



and marls covering the southern part of Arran may now be 

 regarded as undoubtedly of Triassic age. 



(2) The fossiliferous patches of Rhaetic and Lower Liassic strata 



found in the agglomerate indicate the former extension of 

 these formations in the South-west of Scotland, while the 

 sequence of (a) red marls at the base, (h) grey marls in the 

 middle, (c) dark shale and limestone at the top, recalls the 

 development of these formations in the North of Ireland and 

 in South Wales. 



(3) The fossiliferous patches of Upper Cretaceous limestone and 



chert show that strata of that age once extended into the 

 basin of the Clyde, and no doubt covered the surface of the 

 area on which this Arran volcanic focus appeared. The huge 



