378 RECEXT WOEK OF THE GEOLOGICAL STJRVEr 



30. Eepoet on the Receis^t Woek of the Geological Suevey in the 

 NoETH-WEST Highlands of Scotlakd, based on the Field-notes 

 and Maps of Messrs. B. K. Peach, J. Hoen"e, "W. Gucor, 

 C. T. Clough, L. HiyxivfAT^, and H. M. Cadell. (Eead April 25, 



1888.) 



(Communicated by A. Geikie, LL.D., F.R.S., Director-General.) 

 Contents. 



Page 



Introduction 379 



Pretious Literature 379 



I. Arcilean E.0CKS 387 



1. Original types of gneiss 387 



2. Unf oliated igneous rocks in original gneisses 388 



3. Evidence of mechanical movements in the formation of the original 



gneisses 388 



4. Igneous rocks injected into the Archaean gneiss after the first 



foliation and prior to the later Pre-Cambrian movements, {a) 

 basalt-rocks, {h) peridotite dykes, (c) microcline-mica rocks, (d) 

 granite 389 



5. Later Pre-Cambrian movements and their direction 391 



6. Effects of these movements on the intrusive dykes 391 



7. Effects of these movements on the gneiss 395 



8. Evidence proving the Pre-Cambrian age of these movements 399 



9. Summary of the foregoing researches in the ArchjBan rocks 399 



H. Cambrian Formation. 



1 . Denudation of the Pre-Cambrian land surface 400 



2. Order of succession and thickness of the strata in the Parph dis- 



trict 401 



3. Succession and thickness in Assynt 401 



4. Succession and thickness in Loch-Broom d istrict 402 



5. Formation of outliers of Cambi'ian strata in Post-Cambrian and 



Pre-Silurian time by folding and denudation 402 



III. Silurian Formation. 



1. Uniformity in the order of succession 403 



2. Subdivision of " pipe-rock " and the lowest group of limestone ... 403 



3. Physical conditions during deposition of Silurian strata and 



horizon of the latter 405 



IV. Igneous Eocks in Cambrian and Silurian Formations. 



1. Evidence of their intrusive character 408 



2. Horizons 408 



3. Area of distribution 409 



4. Macroscopic characters 409 



5. Contact-metamorphism 410 



6. Date of intrusion prior to Post-Lower-Silurian movements 411 



V. Physical Eelations of the Strata between Eriboll and Ulla- 



pool. 



1. Modification of two inferences announced in former official report 411 



2. Classification of terrestrial movements 412 



3. Chief maximum thrusts 412 



4. Features characteristic of the maximum thrusts 413 



5. Horizontal sections illustrating the physical relations of the strata 



along the line of complicated structm-e between EriboU. and 

 UUapool 414 



