40 ME. A. HAEKEE ON THE GEOLOGICAL [Feb. I906, 



4. The Geological Stetjcttjee of the Sguee of Eigg. By Alfred 

 Haekee, M.A., F.B.S., F.G.S. (Eead December 6th, 1905.) 



[Plates III & IV.] 



Contents. 



Page 



I. Introduction 40 



II. General Structure of the Pitchstone-Complex 43 



III. Fragmental Accumulations and Fossil Wood 52 



IV . Concluding Considerations 64 



I. Inteoduciion. 



The Tertiary igneous rocks of the Inner Hebrides have from time 

 to time engaged the attention of many eminent geologists ; and the 

 results of their labours, interpreted by their skill and insight, have 

 become part of the common stock of British geology. In certain cases 

 the investigation has been conducted on an extended scale. This is 

 true more especially of the work of Macculloch in the earlier days, 

 and of Sir Archibald Geikie and Prof. Judd among those who are 

 still with us. Nevertheless, it is only recently that any consider- 

 able part of that large and complex area has been mapped with 

 the close attention to detail requisite in a complete geological 

 survey. Even apart from the time demanded by such a minute 

 examination of the ground, the large-scale Ordnance maps which 

 make it possible have been issued only within the last few decades. 

 Thus, in the ten years which the present writer has spent on this 

 work, it has been his good fortune to enjoy facilities denied to his 

 predecessors, besides benefiting by the fruits of their labours in the 

 same field. Fortified by these advantages, he has been enabled to 

 pass with less diffidence from observation to inference, even when 

 the latter is at variance with the views of geologists of much wider 

 experience. For, as might be anticipated, the results of the detailed 

 survey, while generally confirming the conclusions of the recognized 

 authorities, have sometimes extended, restricted, or modified them, 

 or have even led to a decided difference of opinion. 



The individual questions on which such difference of opinion arises 

 are not many, but some of them have far-reaching consequences. 

 They are, in all cases, questions the settlement of which demands 

 both close examination of the ground and comparison of different 

 parts of the region ; and this is doubtless the reason why they have 

 not been raised, at least in any very definite form, until the present 

 time. 



The most important modification of hitherto received opinion in 

 consequence of the results of the survey, is the recognition of the 

 intrusive nature of a large part of the rocks which have been 

 generally regarded as extruded lavas. The rocks in question 

 include fully half of those which build up the ' basalt-plateaux ' 

 constituting the greater part of the Inner Hebrides. As illustrating 



