Iviii PBOCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. Ixxiii^ 



In the meantime Jucld had quitted the Sm-vev, and present!}' 

 found himself in a position to resume independent work in the 

 field. He chose as a promising subject of study the Secondary 

 rocks of Scotland. Beginning with the isolated and little-known 

 exposures of these strata on the North-East coast, he was able 

 after two years of work to make out the true succession and corre- 

 lation of the several formations, ranging from the Trias to the' 

 Upper Oolites. He next transferred his attention to the West 

 Coast and the Inner Hebrides ; but there he soon became absorbed 

 in a new interest. The Mesozoic rocks of the west have been 

 buried under great Hoods of lava of Tertiary age, and are only 

 partially exposed as the result of profound erosion in conjunction 

 with plateau-faulting. At certain centres, too, masses of Tei-tiary 

 plutonic rocks have broken through, and now build the mountains 

 of Skye, Hum, and Mull. Little systematic Avork had been done 

 upon these late igneous rocks since the pioneer days of Macculloch, 

 and Judd threw himself into the task with characteristic energy. 

 It was no liglit undertaking, for the area is large, much of the 

 ground is not easily accessible, and no good topographical maps 

 were then in existence. As the result of his investigations, he was 

 led to regard the volcanic rocks of the Inner Hebrides as the 

 products of five great volcanoes, the much-eroded cores of which 

 are now represented by the chief plutonic complexes of the region. 

 He recognized further a certain succession in time among the 

 volcanic rocks, acid lavas and agglomerates being succeeded by 

 basic. If those who have followed him in the same field, Avorking 

 under more advantageous conditions, have not confirmed all his 

 conclusions, the}' have still recognized their great indebtedness to 

 him who led the way. His results will remain an imjwrtant con- 

 tribution to the ultimate solution of the j^i'oblem, as Avell as a 

 memorable example of a generalization boldly conceived and 

 laboriously worked out. 



The memoir which was the outcome of these researches, published 

 in the Quarterly Journal of the Geological Society in 1874, 

 atti'acted the notice of some of the leading geologists of the day, 

 and in this way the author made the acquaintance of Sir Charles 

 Ly ell and Scrope, and later also of Darwin. The friendship and 

 encouragement of these veterans Avas of great value to the younger 

 man. It was under Scrope's auspices that he enlarged his know- 

 ledge of volcanic phenomena by A'isits to the active and extinct 

 volcanoes of Italy, Hungary, and Bohemia, the results of Avhich 



