276 Reviews — Geology of Central Ross-sJdre. 



The phj'sical conditions would seem to have been somewhat as 

 follows: — Owing to elevation in late Niagara times, the sea with- 

 drew towards the north, and an inland arm of the northern sea was 

 placed in imperfect communication with the outer ocean. Chemical 

 precipitation of the carbonates took place, followed by deposition of 

 the sulphates as gypsum. Later, communication with the ocean 

 closed, the temperature of the waters of the basin rose, and anhydrite 

 began to form. At a still later stage lower temperatures prevailed, 

 probably because of the entrance of ocean waters, and continuous 

 deposition of gypsum ensued. The concentration of sodium salts 

 became so great that part of the sodium ions was precipitated in the 

 form of double sulphate. It is still an open question whether 

 evaporation reached the stage of the deposition of the chlorides. 

 When, finally, deeper-water conditions again prevailed, carbonates 

 and traces of sulphates were thrown down, and formed the limestone 

 which now represents the highest beds of the Silurian in Manitoba. 



To summarize, the following conclusion of general applicability 

 may perhaps be legitimately derived from the study of a particular 

 gypsum-anhydrite association. While secondary transformations are 

 possible at considerable depths, and also at the surface, the general 

 character of gypsum-anhydrite deposits may be accounted for most 

 directly, and with least difficulty, as due to original deposition. This 

 applies most obviously in cases where the bedding-plane defines with 

 fair accuracy the contact between anhydrite and gypsum. Where 

 anhydrite occurs in masses irregularly distributed through gypsum 

 rock, transformation processes at or near the surface have played 

 a relatively greater part ; but direct geological evidence has yet to be 

 adduced before the theory can be accepted that transformation of 

 gypsum to anhydrite, at great depths below the surface, takes place 

 to such an extent as to be of geological importance. 



liE'VIE^WS. 



I. — Memoies of the Geological Sukvky- of Scotland. Geology 

 OF Central Koss-shire (Explanation of Sheet 82). By B. N. 

 Peach, LL.D., F.R.S., John Horne, LL.D., F.R.S., and others ; 

 with Petrological JN'otes by J. S. Flett, D.Sc, LL.D., F.R.S. 

 8vo; pp.vi, 114. Edinburgh, (1913) 1914. London: T.Fisher 

 Unwiu, 1 Adelphi Terrace, W.C. Memoir, 25. 3d. ; map, 25. 6d. 

 rilHE area included in Sheet 82 is approximately 429-|- square miles 

 J_ in extent ; about 2^ square miles of salt water at the head of 

 Loch Carron enter into the limits of the map. With the exception of 

 a small part of Inverness-shire in the south-east corner, on either side 

 of Glen Strath Farrar, the whole map falls within the County of Ross. 

 This is a typical Highland area, in which cultivation and popula- 

 tion are reduced to a minimum and confined to the seaboard and 

 a few spots along the larger river-valleys. The ground is mountainous, 

 wild, and inaccessible, and is given up to deer forest and grouse moor, 

 with small and decreasing areas of sheep-grazing at Kinlochewe, 

 Loch Carron, and Scardz'oy. 



