556 Geological Society : — 



constitution CI CI 



p_0-Cl P-S-Cl 



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CI CI 



and that the phosphorus in these bodies is to be regarded as a triad. 

 The author concludes by discussing Buff's hypothesis, that the 

 specific volume of an element varies with its chemical value ; and 

 he shows that, in the case of phosphorus, there are no reasons for 

 the belief that this element has a variable specific volume. 



GEOLOGICAL SOCIETY. 



[Continued from p. 413.] 



January 27, 1875. — John Evans, Esq., E.K.S., President, 

 in the Chair. 



The following communications were read : — 



1. "On the Structure and Age of Arthur's Seat, Edinburgh." 

 By John W. Judd, Esq., E.G.S. 



The author said that Arthur's Seat, so long the battle-ground of 

 rival theorists, furnished in the hands of Charles Maclaren a 

 beautiful illustration of the identity between the agencies at work 

 during past geological periods and those in operation at the pre- 

 sent day. 



One portion, however, of Maclaren's masterly exposition of the 

 structure of Arthur's Seat, that which requires a second period of 

 eruption upon the same site, but subsequent to the deposition, the 

 upheaval and the denudation of the whole of the Carboniferous rocks, 

 is beset with the gravest difficulties. The Tertiary and Secondary 

 epochs have in turn been proposed and abandoned as the period of 

 this supposed second period of eruption ; and it has more recently 

 been placed, on very questionable grounds, in the Permian. 



The antecedent improbabilities of this hypothesis of a second 

 period of eruption are so great, that it was abandoned by its author 

 himself before his death. A careful study of the whole question by 

 the aid of the light thrown upon it in comparing the structure of 

 Arthur's Seat with that of many other volcanoes, new and old, 

 shows the hypothesis to be alike untenable and unnecessary. 



The supposed proofs of a second period of eruption, drawn from 

 the position of the central lava column, the nature and relations of 

 the fragmentary materials in the upper and lower parts of the hill 

 respectively, and the position of certain rocks in the Lion's Haunch, 

 all break down on reexamination ; while, on the other hand, an 

 examination of Arthur's Seat, in connexion with the contemporaneous 

 volcanic rocks of Forfar, Fife, and the Lothians, shows that in the 

 former we have the relics of a volcano which was at first submarine 

 but gradually rose above the Carboniferous sea, and was the product 

 of a single and almost continuous series of eruptions. 



