W. B. Wright — The Drumlins of South Donegal 153 



of junction. That the granite has exercised a distinct contact action 

 on the auriferous series is not generally recognized. The 

 accompanying dykes are sometimes considered to be a later series, 

 where they cut both the granites and the hornblende schists, but this, 

 of course, is not a necessary assumption, for practically all granites 

 are cut by dykes belonging to the same general series of intrusions. 

 The granites have received a little petrographical treatment, but 

 no classification of them into groups has been attempted. The 

 accompanying dykes consist of fine-grained granite, granite porphyry, 

 quartz porphyry, and 'felsite'. For the most part they follow 

 the direction of foliation or are slightly oblique to it. 



Granites of more than one age are occasionally recognized in the 

 same field. Thus, near Mt. Percy in the Edjudina District, North 

 Coolgardie Goldfield, Maitland describes a foliated granite (apparently 

 intrusive into greenstone) and a later unfoliated granite.^ In the 

 North Murchison Goldfield, also, Gibson considers the granites of two 

 ages, a younger undoubtedly newer than the greenstones, and an 

 older of doubtful age.^ In the Stannum Group of the Woodgina 

 Tinfield, Pilbara Goldfield, Maitland recognizes an area of intrusive 

 porphyry which is of later date than the greenstones and older 

 than the granite and pegmatite veins. ^ 



The close association between the intrusion of the granites and the 

 deposition of the gold has been frequently, if not very clearly, 

 indicated. The majority of the smaller goldfields are situated within 

 the contact aureole of the granites, and many reefs are directly 

 associated with dykes of 'felsite'. In a few fields the gold deposits 

 are found within the granite itself. In other cases it is found 

 that the deposits are intersected by dykes of acid rock.* The 

 close association of tin and tantalum with albite - pegmatite is 

 very clear. 



[To he concluded in our next Number.) 



III. — The Drijmlin Topography of South Donegal. 



By W. B. Weight, B.A., F.G.S. 



PLATES VIII AND IX. 



(The observations relating to the Pettigo area are communicated with the 

 permission of the Director of the Geological Survey of Ireland.) 



MOST people who have lived in strongly glaciated countries are 

 familiar with the topogi-aphic features known as druralins. 

 They are more or less elongated hills of boulder-clay with their long 

 axes parallel to the direction of ice-motion. The literature dealing 

 with them is extensive, but for the most part rather unsatisfactory. 

 Their mode of formation is entirely a matter of speculation and is 

 likely to remain so. There is every reason to believe they are deep- 

 seated products of the ice, so that observation of the process in modern 

 ice-sheets is impossible. The only available means of getting at the 



1 Bull, xi, p. 30, 1903. ^ -j^^n ^iv, p. 13, 1904. 



* Bull, xxiii, p. 61, 1906. * Gibson, Bull, xii, p. 11, 1904. 



