Vol. 57.] MESOZOIC KOCKS IN THE ISLAND OF AERAN. 229 



masses of Mesozoic shale and of hard Chalk now found in the 

 vent must have fallen down from above into the vent, as has 

 happened in the Palaeozoic strata in some of the Carboniferous 

 vents in Scotland. 



(4) The igneous rocks of the vent are thus of post-Cretaceous age, 



and may be confidently assigned to the great Tertiary Volcanic 

 Series of this country. 



(5) From the absence of recognizable blocks in the agglomerate 



belonging to the formations intervening between the Lower 

 Lias and the Chalk, it may be inferred that these intervening 

 formations were never deposited in this region, or had been 

 removed by denudation before Cretaceous time, as in the 

 North of Ireland. 



(6) The geological features of this volcanic area furnish im- 



pressive testimony as to the vast amount of denudation that 

 has taken place in the South of Scotland since the period of 

 Tertiary volcanic activity .'^ 



Part II. Pal^ontological Notes. 

 [Plate IX.] 



The peculiar circumstances under which were found the fossils 

 that form the subject of these notes have been dealt with by my 

 colleagues, and it will be sufficient to state here that the masses of 

 rock from which they were obtained do not appear to be in situ, 

 but are believed to be fragments of strata once existing in the 

 district but now entirely removed by denudation. 



1. Ehsetic Series. 



The first collection of fossils supposed to be of Rhaetic age and 

 obtained by Mr. Macconochie from Shiskine in May 1900, was for- 

 warded to me for examination. The fossils themselves were in a 

 dark, almost black shaly limestone, were very obscure, and their 

 age was uncertain, for they proved to be too fragmentary to allow 

 of definite specific determination, and it seemed possible that they 

 might after all be of Carboniferous age. The search was continued 

 by Mr. Macconochie, and a further collection was obtained and for- 

 warded to me. The occurrence of undoubted specimens of Avicula 

 contorta, together with other forms, proved beyond doubt the 

 Khaetic age of the beds. A brief account of this discovery was 

 published in the Director-General's Summary of Progress of the 

 Geological Survey for 1899, p. 133. 



1 The fossils described by Mr. E. T. Newton in Part II were mainly collected 

 by Mr. Macconochie. 



