82 Notices of Memoirs — Dr. G.F.Matthew — Cambrian Genera. 



has increased very considerably ; but tbere are also plenty of others 

 in which this is not the case, even with highly altered rocks close to 

 the contact, the normal excess of potash over soda having remained 

 undisturbed ; and the evidence, as will be seen, is rendered all the 

 more contradictory by the fact that in a given vertical section of 

 beds we may have a rock quite near the Whin, showing this 

 chemically unchanged condition, whilst another one, further away 

 from contact, shows a great increase of soda relatively to the potash. 

 As previously pointed out, the rocks along the Whin Sill are not 

 specially favourable for the study of the chemical aspect of the 

 metamorphism, inasmuch as the igneous mass is intruded parallel 

 to their strike, and we cannot take any one bed at a distance and 

 follow it gradually up to the contact. All we are able to do is to 

 rely on the fact that, apparently without any exception, the normal 

 shales of the Carboniferous show an excess of potash over soda 

 within certain limits. All the trustworthy chemical evidence 

 available shows this to be the case, and I have myself confirmed 

 it by large numbers of careful determinations, published and 

 unpublished, on specimens from various localities ; the two latest 

 being a fireclay and a shale which I took from the neighbourhood 

 of Bardon Mill, near to the exposure of the Whin Sill and its 

 contact-rocks, but quite outside the area of its metamorphic action. 

 The alkalies contained are respectively : — 



Potash 2-62 per cent, and 2-66 per cent. 



Soda 0-98 ,, and 1-24 



The three analj/ses given above of calcareous adinoles are all striking 

 instances of a large increase in soda. The total alkali-contents are 

 all three high, though not higher than may be seen in some cases of 

 chemically normal shales. But soda far exceeds potash in all of 

 them. No shales of similar composition exist outside the contact- 

 zone, and however we may explain the transfer of soda, we cannot 

 very well deny its occurrence. This increase of soda, as a chemical 

 fact, is accompanied by the mineralogical fact of the appearance 

 of albite in the altered rock. Had we these cases only before us, 

 there would not seem to be much difiiculty in accepting the 

 statements of previous observers on the subject. 



{To be continued.) 



I. — Some Characteristic Genera of the Cambrian.^ By G. F. 

 Matthew, LL.D., D.Sc, F.E.S.C. 



THE paper gives in brief the history and use of several generic 

 names, and the distribution of certain species to which they 

 have been applied. These genera have an important bearing on the 

 antiquity of the Olenellus Fauna. Bathyiiriscus, Meek, known as 

 a Middle Cambrian genus in Montana and Nevada, occurs in the 

 Olenellus Fauna of Eastern North America. It is nearly allied 

 1 Paper read in Section C (Geology), British Association, Toronto, August, 1897. 



