22 DR GEIKIE ON THE HISTORY OF VOLCANIC ACTION 



liypogene activity is specially prone to manifest itself. From early geological times this 

 activity has been displayed in various characteristic forms. Hence, within the geological 

 records of Britain there has been preserved a more continuous and complete chronicle 

 of volcanic phenomena than, so for as I am aware, has yet been discovered in any tract 

 of similar size on the face of the globe. The rocks of the country have been investigated 

 so long and so minutely that their general chronological succession has been accurately 

 ascertained, and hence the precise horizon of each volcanic episode can be definitely fixed. 

 The varying phases of eruptivity in different geological periods can be made out, and a 

 large body of evidence can thus be amassed bearing on the general question of the past 

 history of volcanism. 



Taking the broadest view of the subject, we find that the volcanic history of Britain 

 naturally divides itself into two widely separated periods. The first of these embraces 

 the vast Palaeozoic ages ; the second falls entirely within older Tertiary time. Between 

 these two periods comes the prolonged interval marked by the whole series of Mesozoic 

 formations in which, save at their base, in the lower Triassic rocks of Devonshire, no trace 

 of contemporaneous volcanic action is known. It is to the records of the second of the 

 two great volcanic eras that the present memoir is devoted. 



Before entering upon the detailed investigation, it may be useful to sketch briefly 

 what has been the progress of opinion regarding the phenomena to be discussed. The 

 basaltic cliffs of Antrim and the Inner Hebrides had attracted the notice of passing 

 travellers, and their striking scenery had become more or less familiar to the reading 

 public, before any attention was paid to their remarkable geological structure and history. 

 In particular, the wonders of the Giant's Causeway and the Isle of Staffa had already 

 begun to draw pilgrims, «ven from distant countries, at a time when geology was still in 

 its earliest infancy. The scientific tourist of those days who might care to look at rocks, 

 was, in most cases, a mineralogist, for whom their structural relations and origin were 

 subjects that lay outside of the range of his knowledge or habits of thought. One of 

 the earliest traces of an intelligent appreciation of some of the geological interest of the 

 region is to be found in Whitehurst's Inquiry into the Original State and Formation 

 of the Earth (2nd edit., 1786), where a good account of the basalt-cliffs of Antrim is 

 given, and where the basaltic rocks are regarded as the results of successive outflows of 

 lava from some centre now submerged beneath the Atlantic. More important are the 

 observations contained in two letters of Abraham Mills, published in the Philosophical 

 Transactions for 1790. This writer had been struck with the dykes on the north coast 

 of Ireland, and was led to examine also those in some of the nearer Scottish islands. 

 He believed them to be of truly volcanic origin, and spoke of them as veins of lava. 

 A few years later, Faujas St Fond made his well-known pilgrimage to the Western Isles. 

 Familiar with the volcanic rocks of the Continent, he at once recognised the volcanic origin 

 of the basalts of Mull, Staffa, and the adjoining islands. His Voyage, published in Paris 

 in 1797, may be taken as the beginning of the voluminous geological literature which has 

 since gathered round the subject. Three years afterwards (1800) appeared Jameson's 



