PRKSIDENT S ADDRESS. IX. 



general principles of eartli foldings and movings, are very 

 valuable to the student of the subject. He regards the High- 

 land regions, excluding the granite district of the Grampians, 

 as the worn-down stump of a great mountain mass, and points 

 out that many, if not all, of the dispositions of strata which 

 have been worked out by Heim for the chain of the Alps recur 

 in the Highlands, only, as is but natural, in a state somewhat 

 more difficult to recognize. 



Dr. Callaway, taking the district of Assynt as his special 

 example, concludes that what has been considered the Silurian 

 gneiss is really an immensely older formation ; that, in fact, it is 

 Pre-Cambrian, though newer than the Hebridean gneiss. The 

 sedimentary rocks deposited on the upturned faulted and 

 denuded edges of these ancient gneisses are Sandstone, Quart- 

 zite, and Dolomite, but there is no evidence as yet as to their 

 age. The whole mass of rocks was then by great and wide- 

 spread earth movements folded back on itself, crumpled, faulted, 

 and denuded. The crumpling and faulting extends in some 

 places even to microscopic dimensions, and some slides which I 

 have prepared from specimens collected by Prof. Lapwortli in 

 the neighbourhood of Loch Erribol show the efiects of the 

 pressure to which thej' have been subjected in another most 

 interesting manner. A few felspar crystals are still recog- 

 nisable, and in some cases the twin lamellae are not straight 

 and tolerably parallel as in the undisturbed state, but are 

 contorted and twisted out of place. It is, perhaps, the most 

 interesting point in the purely petrological consideration of the 

 subject, that the evidences of the enormous pressure to which 

 the rocks have been subjected, and under which they have 

 apparently flowed like some viscous substance, are so marked. 

 The finer constituents are in many instances arranged in lines 

 round the larger quartz grains, in such a manner as to 

 perfectly simulate the so-called fluxion structure observed in 

 rocks which have flowed in a molten state. The enormous 

 extent of some of the great overthrows of the Highlands must 

 astonish us. Systems of strata have been thrown into folds a 



