398 TRANSACTIONS OF SECTION C. 



where the acid rocks occur, and the material deposited to form the present 

 remarkable stream. It has also been objected that none of the blocks are 

 ice-scratched, but this is not to be expected owing to the exceptional fissility of 

 liparite and its rapid degradation under weathering influences — the author has 

 never seen an ice-scratched boulder in Iceland. 



I. Th. Thoroddsen. 'Island: Grundriss der Geographic und Geologic.' 

 No. 152. Pet. Mitt. 1905. 



II. H. Pjetuess. ' Island : Handbuch der Eegionalen Geologic.' 1910. 



III. C. W. Schmidt. ' Der Liparite Islands in geologischer und petro- 

 graphischer Beziehung.' ' Zeit«chrift der Deut. geol. Gesell.' Vol. xxxvii. 

 1885. 



IV. Sir A. Geikie. ' Ancient Volcanoes of Great Britain.' Vol. ii. 1897. 



3. The Petrology of the Arran Pitchstones. By Alexander Scott, 



M.A., D.Sc. 



Although the Arran pitchstones are so widely known, no extensive examina- 

 tion of them has ever been made. The intrusions, which number about eighty, 

 may be divided into the following groups : — 



(a) Non-porphyritic glasses with abundant microlites which are generally 



hornblende. These are chiefly found in the district round the coast 

 and include the Corriegills and Monamore Glen occurrences. 



(b) Pitchstone-porphyries with large phenocrysts of quartz and felspar and 



scarce augite and with hornblendic microlites. This group includes 

 many of the dyke-rocks intrusive into the Goatfell granite, 

 (f) Pitchstone-porphyries with phenocrysts of felspar and pyroxene and sub- 

 ordinate quartz. The pyroxene includes both augite and enstatite, and 

 scarce crystals of an iron-rich olivine are also found. ^Microlites of 

 pyroxene and of hornblende occur. This group is typical of the intru- 

 sions of the south end of the island. 

 (fl) More basic type with scarce phenocrysts and great abundance of 

 pyroxene microlites. This group is represented by two occurrences in 

 Glen Cloy and several around the great Tertiary volcanic vent. 

 Analyses have been made of each type, and the results show the existence 

 of considerable variation in composition. 



An attempt has been made to determine the cooling histories from the 

 examination of the field relations and the microscopic structures of the various 

 types, and also to indicate the conditions which are responsible for such a large 

 development of glassy intrusive rocks. 



FRIDAY, SEPTEMBER 8. 



Joint Meeting with Section E. 



The following Paper was read : — 



The Physical Geography and Geology of the Northern Pennines. 

 By Dr. A. Wilmore. 



This paper attempts a brief summary of the structure of the Northern 

 Pennines for geologists and geographers, especially for those who are interested 

 in the relation of geographical form to geological structure. It is, for the mo.st 

 part, a re-statement, and advances little that is new ; but it is thought that the 

 present visit of the Association to the North may be a fitting opportunity to 

 summarise our knowledge of the structure of an interesting region, especially 

 as considerable progress has been made in our detailed knowledge of the 

 Northern Pennines since the visit of the Association to Newcastle in 1889. 



By ' The Northern Pennines ' as treated in this paper, we mean that well- 



