310 Prof. Johnston Lavis — Formation of Minerals — 



at a temperature so low as to be insuflScient to carbonize or even 

 discolour the organic matter of bone, that is at a temperature 

 considerably below that of an ordinary baking oven. 



A. Scacchi was the first to draw attention to certain enclosures 

 in the grey tuffs of the Campania, which I have shown to be the 

 representatives of that enigmatical rock the piperno of Pianura, 

 and to hold chronologically and stratigraphically the same relative 

 position. To denote the peculiar structure due to the enclosures of 

 different texture of these as well as rocks from different psirts of the 

 world, I have proposed the adjective pipernoid, and references to 

 this clastic volcanic rock in several of my papers is denoted as 

 pipernoid tuff. 



A, Scacchi supposed this tuff to be the result of mud streams 

 that issued from a wreath of volcanic vents scattered all along the 

 edge of the Campanian plain, where limited by the limestone hills ; 

 and the metamorphosed limestone enclosures he considered as true 

 ejected blocks, or, as Prof. Lacroix calls them, enclaves. I have 

 been able to refute these views, for the following reasons, as con- 

 cisely summarized below ^ : — 



(1) The pipernoid tuff is a typical andesitic or trachytic scoria, 

 pumice, and dust deposit, and bears no relationship whatever to the 

 clays of mud volcanoes. 



(2) To have produced such deposit of it, dozens of months would 

 .have been required, not only where A. Scacchi locates them but 

 over hundreds of square miles, and often at the tops and shelves 

 of calcareous mountains, unless we were to admit the mud to have 

 flowed uphill. 



(3) The metamorphosed limestone fragments only occur in the 

 pipernoid tuff where this forms a talus against a limestone hill, and 

 are distributed in the tuff in curved wedge-shaped bands just as any 

 fragments ai"e arranged in a talus by the law of angles of repose. 



(4) The greater thickness of the tuffs at the foot of the limestone 

 hills is simply due to the talus formed at their feet by the washing 

 down of the mantle of fragmentary material that covei'ed them after 

 their fall from the air at the time of the eruption. 



(5) That the same arguments as apply to the number of volcanic 

 vents also apply to the existence of fluoriferous fumaroles or springs, 

 as suggested by A. Scacchi. 



It is evident, therefore, that in such a tuff, after its journey through 

 the air, its fall on the surface of the country, and its subsequent 

 transport to lower levels by water, that no heat above that of the 

 'Surrounding atmosphere could remain, of what existed at the volcano 

 from which the ejecta had been derived, to act upon any inclusions 

 in such a tuff. If any doubts on this point existed, the uncarbonized, 

 unroasted bones included in the tuff would finally dispose of them. 



The bone in question I easily recognized as the upper part of 

 a tibia, probably of Cervus, and this diagnosis was subsequently 



' See H. J. Johnston -Lavis : British Association Eeports for 1888-89-90-92, 

 and Notes on Pipernoid Structure of Igneous Eocks, "Natm-al Science," vol. iii, 

 No. 19, September, 1893, pp. 218-221. 



