Reviews — Prof. Hedclle — Geognosy of Scotland. 373 



analj^ses that the Durness and Assynt Limestones are very distinct 

 in chemical composition, the latter being a typical Dolomite, contain- 

 ing about 45 per cent, of carbonate of magnesia, while the former 

 is an ordinary Limestone, containing only about Z\ per cent, of 

 magnesian carbonate. Several other distinctions between the two 

 limestones are pointed out, and the author contends that these two 

 rocks, hitherto united by all investigators, are totally distinct in 

 geological age — " Different in composition, different in structure, 

 pregnant with fossils, more highly metamorphosed, associated with 

 newer rocks, altogether out of place, — it will need absolutely new 

 evidence before our theoretical geologists are warranted in declaring 

 this (Durness) Limestone to be a chip off" that old block of (Assynt) 

 Dolomite, which now stands above it. And if the two ' Limestones ' 

 be different, then the whole fabric of Murchison's correlation of the 

 rocks which overlie the Dolomite falls to the ground." 



To this sweeping conclusion the average reader of Prof. Heddle's 

 work will probably oppose the very natural suggestion that, although 

 the Durness fossiliferous Limestone may not be the exact counter- 

 part of the Lower or true Dolomitic Limestone of Assynt, as hitherto 

 believed ; yet it may perhaps be the representative of the Upper 

 Assynt Limestone — the Ledbeg marble i which, as Dr. Anderson has 

 shown (pp. 315 and 316), agrees almost exactly in chemical composi- 

 tion with the Durness bed, and is placed by Dr. Heddle himself in 

 the Quartzitic series, between the igneous rocks and the Upper 

 Gneiss : and if this be the case, the argument of Murchison and 

 Geikie stands unaffected. 



This suggestion, however, again lands us in some awkward diffi- 

 culties, and the new school of Archgean geologists may well draw 

 encouragement from the fact that the two most eminent chemists on 

 opposite sides of the Atlantic, who have largely devoted their own 

 special science to the study of matters more or less connected with 

 geology, should have so strongly pronounced in favour of their views. 

 And when the history of their anticipated Highland conquest comes 

 to be written. Prof. Heddle and his bold and brilliant contributions 

 to the controversy will hold a prominent and honoured place therein. 

 Even the peaceful students of the gradual development of geological 

 discovery, who look upon this conflict from a distance, and watch the 

 alternate successes of the opposing forces of long-established authority, 

 and pre-conceived theory, cannot but feel grateful to Prof. Heddle 

 for having taught them that the Highland question is a vastly greater 

 problem than it appears from a distance. It appears impossible to 

 resist the conclusion that when the subject is attacked earnestly in 

 the good old-fashioned way of mapping every foot of the disputed 

 ground, and allowing the facts to speak for themselves, the sequence 

 will eventually be found to be " clear and simple, and quite 

 analogous to those of other mountain regions," and that when all 

 the evidence is before us, this old mountain region, like that of the 

 Alps themselves, will, even in its difficulties and anomalies, afford 

 another and a " most triumphant proof of the value of the old long- 

 established principles of British geology." 



