1 66 The Scottish Naturalist. 



zoic age, readily recognisable as such by anyone who cares to 

 examine it. 



It occurs in this wise. A breccia, that is a confused mass of angu- 

 lar fragments of volcanic rocks, which probably formed part of the 

 crater-cone of a volcano of the Old Red Sandstone age, near Tay 

 Bridge, Newport, Fife, is mostly composed of masses of all sizes of 

 quartz-andesite, one of the more acid members of this intermediate 

 group of volcanic rocks. 



In many of the large blocks of the quartz-andesite (or as peno- 

 logists call it, Dacite), are hollows of considerable capacity, relatively 

 to the size of the block. It is in one of these hollows, in a huge 

 block on the plain of the beech, that the glass occurs. It mainly fills 

 the hollow ; but is surrounded with a considerable quantity of a 

 white powder, which is the glass in its last stage of decay. 



That distinguished geologist, Prof. John W. Judd, F.R.S., of the 

 Royal School of Mines, says of this glass : " It is a unique instance, 

 in the case of a rock of such great antiquity," that "some portions of 

 the glassy base are seen to be quite as free from alteration as any 

 Tertiary or Recent obsidian," and further adds that "most striking 

 and beautiful is the pertitic structure of this remarkable rock. I 

 know of no glass, ancient or modern, which exhibits this structure in 

 greater perfection. This remarkable rock must be classed as a 

 porphyritic and pertitic mica-dacite glass. It appears that this vit- 

 reous variety occurs in scattered nests in the midst of the ordinary 

 stony form. I have seen in the lava streams of Lipari similar angular 

 masses of glass, enclosed in the stony rhyotites ; and the appearances 

 in both the ancient and the recent rocks suggest that a brittle glassy 

 rock had been broken up and entangled in a more stony cooling 

 mass, that had assumed a stony character. Subsequently this lava 

 itself appears to have been broken-up by a volcanic vent being 

 opened below it; and its fragments thus became enclosed among the 

 ejecta-ofthe later volcano." To put it briefly, Professor Judd finds 

 no essential difference between these modern glassy rocks, upon 

 which he is so famous an authority, and this ancient glass, which has 

 been discovered in the centre of the district of "The East of Scot- 

 land Union of Naturalists' Societies." 



