of some Sedimentary Rocks. 237 



scribedj is Lower Silurian ; it is purplish-blue in colour, com- 

 pletely opake, with a feeble glimmering lustre on its cleavage 

 planes, which are nearly at right angles to the bedding density 

 2-884. No. II. is an Upper Silurian slate from Westbury, 

 Eastern Townships ; it is greenish-blue, with a silky surface, and 

 is translucent on the edges; density 2'711. Both of these are 

 excellent roofing-slates. No. III. is a Welsh roofing-slate closely 

 resembling No. I. in appearance, with a density of 2'824; and 

 No. IV. is from the quarries of Angers in France, very like No. II., 

 but more translucent, with a pearly lustre on its cleavage sur- 

 faces, and somewhat talcose ; density 2*882. The analyses were 

 made by fusion with carbonate of soda, and the alkalies deter- 

 mined by decomposing a separate portion with a mixture of car- 

 bonate of lime and sal-ammoniac, after the method of Dr. J. 

 Lawrence Smith. 



100-24 99-50 - 10003 100-13 



It is probable from the colour, that a part of the iron in I. 

 and III. exists as peroxide ; traces of manganese were detected in 

 all of them. The last specimen had been exposed to the weather 

 upon the roof of a house for nearly a century, and this may 

 account for the smaller quantity of alkalies which it contains. 

 When finely elutriated, these slates give to the water a distinctly 

 alkaline reaction, and to such a solvent process is to be ascribed 

 the deficiency of alkalies in the schist of St. Nicolas compared 

 with the associated parophitc, with which this reaction is much 

 less distinct. In our Geological Report of last year, from which 

 these analyses are taken, I have had occasion to point out the 

 relation between these slates and the alkaline mineral springs 

 which are so abundant in this region. These waters contain, 

 besides alkaline chlorides, large portions of alkaline carbonates, 

 with borates and silicates, the chlorides frequently constituting 

 the smaller part of the solid contents. Some of these springs 

 are further remarkaljle from the large proportion of potash which 

 they contain, in one instance amounting to one-fourth of the 

 alkaline salts present, when estimated as chlorides of potassium 

 and sodium. 



