372 Reviews — Prof. Seddle — Geognosy of Scotland. 



cinticism of the professed mineralogist ; of its thoroughness and value 

 thei'e can be but one opinion, and the, memoir is probably destined to 

 be the standard guide-book to the mineralogical localities of Scotland 

 for many years to come. 



But as geologists, those parts of the work which treat of the 

 geognosy and geology of the regions described deserve an especial 

 notice from us, and that not only because of the new data they afford, 

 but also from the bold and novel speculative views they contain. 

 Small as is the area hitherto described by the author, he has already 

 broken loose from many of the accepted traditions, and has enun- 

 ciated some of the more advanced views of the newer geological 

 schools to an extent that must be startling — to say the least — to those 

 who hold that the British geological scale is complete, and that the 

 Highland rocks are nothing more than metamorphosed representa- 

 tives of the Silurian sediments of the south. Two instances of this 

 may here be pointed out. 



In the concluding portion of his description of the Shetland Isles, 

 the author, after expressing his general accord with Prof. Sterry 

 Hunt in his well-known generalization that " in altered rocks, the 

 crystalline minerals which are formed may, perhaps, to a certain 

 extent, become to the geologist, what organic remains are in the 

 unaltered rocks — a guide to their geological age and succession," 

 enunciates the opinion that the metamorijhic rocks of Shetland 

 " form a group which occurs nowhere else in the northern division 

 of the kingdom." He sees in Dr. Sterry Hunt's Upper Euronian 

 System a system singularly accordant with the rocks of Shetland, 

 and throws out the hint that the schists of Clova and Portsoy form 

 another series equally accordant with the Taconian. 



In Sutherland — the queen of Scottish counties — Professor Heddle 

 is at his best. Its magnificent scenery, its remarkable mineralogy, 

 and, above all, its unique geological features, seem to have aroused 

 all his interest. He devotes two successive instalments of his woi'k 

 to a description of this county alone. In the first of these, the 

 scenery of the region is described and discussed with the pen of an 

 enthusiast. In the second an extended account is given of its varied 

 geological formations, from the basal hornblendic gneiss of the west 

 to the micaceous gneisses of the interior. As respects the relation 

 of the Hebridean gneisses and the Torridon Sandstone, Prof. Heddle 

 agrees generally with his predecessors. As regards the presence of 

 the quartzites in the Assynt district, and of intercalated dolomitic 

 limestones and marbles, which are succeeded above by the Suther- 

 landshire gneiss, he agrees substantially with Murchison and Geikie, 

 but adds largely to our previous knowledge of the local distribution 

 of these rocks. In the matter also of the so-called igneous rocks he 

 is in general accord with the last-named observers, and adduces so 

 many instances of intercalation that it is almost impossible to 

 avoid the conclusion that we have here a series of contemporaneous 

 volcanic sheets. But as regards the relation between the fossiliferous 

 limestone of Durness and the unfossiliferous limestone of Assynt, 

 Prof. Heddle's ideas are wholly revolutionary. He shows by several 



