The Scottish Naturalist. 165 



habits from any ol the recognised forms of Columbinae. Any one 

 wishing to see a nest could scarcely visit the locality at a wrong time 

 during the season from spring to winter. During winter, as already 

 mentioned, nesting goes on only in mild weather. 



NOTE ON AN ANCIENT VOLCANIC GLASS NEAK NEWPOBT, FIFE. 



By JAMES DURHAM, F.G.S. 



ANYONE that has concerned himself with volcanic phenomena 

 is aware that lavas, when rapidly cooled, form more or less 

 perfect glasses, e.g., obsidian, pitchstone, or trachyte ; just as, when 

 slowly cooled, they form stony rocks, such as andesites and basalts 

 (which are the ordinary road-metals of a great part of the district of 

 the Union) ; or when extremely slowly cooled they form perfectly 

 crystalline rocks, such as granite in the acid series, or gabbro in the 

 basic. 



The capability of cooling into a glass seems to depend to a very 

 great extent upon the quality of the lava. Extremely acid lavas 

 most readily formed the most perfect glasses, often of great extent 

 and thickness ; while basalts became glasses, for the most part, only 

 along narrow lines of contact with other rocks, which rapidly deprived 

 them of their heat by radiation and absorption. 



Students of volcanic rocks of Palseozoic age have always been im- 

 pressed with the apparently entire absence of glasses among the 

 ejecta of these ancient volcanoes, even when the stony lava-streams 

 seemed identical with those of recent eruptions. 



This absence of glass, along with certain differences of mineral- 

 ogical structure, induced one school of geologists to come to the con- 

 clusion that volcanic eruptions in Palseozoic times were entirely 

 different in character from those of Tertiary and Recent ages. 



On the other hand, other geologists continue to maintain that all 

 through the ages volcanoes had behaved just as they do to-day ; and 

 explain the absence of glasses, and the other mineralogical differences, 

 as being the result of changes arising in the rocks through chemical 

 and physical actions, prolonged throughout the ages during which 

 these rocks have been buried in the ground. 



This rock, which I have the honour of exhibiting to you to-night, 

 strikingly confirms the conclusions of the Uniformitarian School of 

 geologists (mainly British), as in it we have a perfect glass of Palseo- 



