DYNAMICAL GEOLOGY. 2/1 



Geikie at first agreed with Edward Forbes as to the geolo- 

 gical age of the basaltic flows in Skye, but further researches 

 led him to form another conclusion, and in 1867 he wrote that 

 all the eruptions of basalt in the Western and the Faroe Isles, 

 as well as those in Iceland, had taken place during the Tertiary 

 epoch, and that the individual outbreaks had been separated 

 by long intervals of time, during which fresh-water deposits, 

 conglomerates, and even thin coal-seams had accumulated. 

 The volcanic flows covered considerable areas and solidified 

 quickly into compact basalt, sometimes to spheroidal or 

 columnar basalt. Forbes had already expressed the opinion 

 that in Scotland it was not a question of submarine but of sub- 

 aerial eruptions, and Sir Archibald Geikie confirmed this view. 



While Geikie was still engaged in his field investigations, 

 Professor Judd published a paper on the extinct volcanoes of 

 the Scottish Highlands, in which he tried to prove that the 

 volcanic outbursts had proceeded from five great central 

 volcanoes. Judd supposes three periods of eruption, the first 

 characterised only by acid rocks (felspathic lavas and granite), 

 the second by basalt and basaltic tuff, and the third by the 

 formation of sporadic volcanic cones of various constitution. 

 Geikie contested these views in a series of papers whose con- 

 tents are comprised in the second volume of his work, The 

 Ancient Volcanoes of Great Britain, published in 1897. 



No basaltic region in the world has been examined and 

 described with the same accuracy as the Western Isles of 

 Scotland. Sir Archibald Geikie has convincingly proved the 

 order of succession of the different contemporaneous flows, 

 the age of the various intrusive sheets and dykes, the occur- 

 rences of fossiliferous strata interbedded between the contem- 

 poraneous basaltic flows, and has also demonstrated the 

 presence of ancient necks and in several places even vestiges 

 of original craters on the surface of the older lavas. Through 

 his exposition of one of the most involved and puzzling pieces 

 of research undertaken in any country, Geikie has thrown new 

 light upon the history of extinct volcanic action. In his hands 

 this typical district of ancient volcanicity has revealed to the 

 geologist many fundamental principles of correlation in the 

 subterranean and surface distribution, and in the consolida- 

 tion of rock-magmas, which are of the highest significance for 

 the study of homogeneous volcanic rock. The diverse and 

 often marvellously beautiful scenic effects produced in the 



