TRANSACTIONS OP SECTION C. 427 



Ichthywmirus communis, from the Lower Lias of Ljniie Regis. The last- 

 named, 520 mm. in length, had been studied in 520 sections taken at equal 

 intervals apart, which revealed in remarkable detail the internal structure 

 with a completeness hitherto unknown. 



Vertebrate Life Zo)ies in the Permo-Trias. By D. M. S. Watson. 



3. The Corrosive Action of certain Brines in Manitoba. 

 By Professor R. C. Wallace, M.A., Ph.D., D.Sc. 



Brine springs issue from Middle and Upper Devonian limestones and dolo- 

 mites at the foot of the Manitoban escarpment. At least eighty brine areas are 

 known, with a total flow — during the dry season — of approximately 500 gallons 

 per minute. The water circulates in the Dakota Sandstone, the basal member 

 of the Cretaceous series, and extends laterally into the Devonian calciferous 

 formations, from which it leaches sodium chloride, disseminated through cer- 

 tain dolomite horizons. The composition of the brines, expressed in percentages 

 of total solids, is very similar to that of sea-water. It is a somewhat purer 

 solution of sodium chloride, and also a more concentrated solution, than sea- 

 water, the percentage salinity being 5 — 7 (sea-water 3'5). 



The salt-flats where the springs reach the surface are devoid of vegetation, 

 :ind studded with ice-carried boulders. These are representative of the pre- 

 Cambrian igneous series of North-Central Canada — granites, gneisses, and 

 ejiidiorites. They have suffered intense chemical disintegration, large boulders 

 having been reduced to half their original size. Different minerals have been 

 affected to different extents, but not even quartz or garnet has escaped cor- 

 rosion. Ferromagnesians have been most intensely affected ; and gneissosc 

 structures, hardly noticeable on un weathered surfaces, stand clearly revealed. 

 The striking difference between the action of these brines and that of sea- 

 water calls for explanation. 



Thiij crusts of salt gather, during the summer months, on the flats and 

 around the boulders. The salt is somewhat deliquescent; and thin films of brine 

 are drawn, by surface tension, over the surface of the boulders. Water in 

 <ontact with the atmosphere is a powerful disintegrant. Alkalies are removed 

 as chlorides or carbonates, and silica and alumina are precipitated as gels, 

 separately or in combination. The gels exercise selective adsorption on the 

 salts of the brine, alkali being taken up and the brine being left richer in the 

 acid radicals. The brine is thereby rendered a more active disintegrating 

 agent, and the process goes on continuously. The function of the dissolved 

 salts is considered to be twofold : (1) they provide a thin film of liquid in 

 contact with atmospheric oxygen ; (2) owing to partial adsorption by colloids, 

 they provide an acid residual solution, which is a powerful corrosive agent. 



The evidences of the corrosive action of sea-water on beach boulders are, 

 no doubt, obscured by mechanical attrition due to wave action. Such corro- 

 sion cannot, however, be compared in intensity with that of the brines. 

 Boulders between high- and low-water mark are alternately submerged and dry 

 to the base — a state of affairs inimical to the persistence of thin films of liquid 

 on the surface of the boulders. The initial conditions are consequently wanting; 

 and the relative immunity of beach boulders from chemical corrosion is due, 

 not to any inability of sea-water to act as a corrosive, but to the absence of 

 favourable conditions for the activity of the solution. 



4. T/te Carboniferous Limestone Zones of N.E. Lancashire. 

 By Albert Wilmore, D.Sc. 



The sequence is well seen in the neighbourhood of Clitheroe, where numerous 

 quarries have been opened up. The lowest beds exposed are near Chatburn mill, 

 and are dark, thinly-bedded limestones with calcareous shale partings. Fossils 

 are very scarce. There is a great thickness of these almost unfossiliferous beds, 

 the top parts of which are dolomitic. 



