T H E 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



APRIL 1854. 



XXXV. On the Composition and Metamorphoses of some Sedi- 

 mentary Rocks. By T. S. Hunt, of the Geological Commission 

 of Canada^. 



IN the Report of Progress of the Geological Survey of Canada 

 for 1851-52, I have described a peculiar metamorphosis of 

 a portion of the Lower Silurian shales at St. Nicolas, on the 

 south side of the St. Lawrence, near Quebec. The recks there 

 exposed have been minutely described by Mr. Logan; they 

 belong to that division of the formation which is known as the 

 Hudson River group, and consist of beds of greenish, quartzose 

 sandstones, from one to three feet in thickness, interstratified 

 with thin layers of greenish, bluish, or reddish shales. The 

 colours of these are probably connected with different states of 

 oxidation of the iron which they contain. The green colour is 

 sometimes seen in small oblong rounded patches in the red shale, 

 and when in a mass of the latter a layer of from half an inch to 

 an inch of somewhat calcareous matter occurs, it is bounded 

 above and below by a portion of green slate, sometimes no more 

 than a quarter of an inch in thickness. In one section near 

 Pointe Levy, the green colour was seen following down a rift in 

 the red slates across the stratification, and spreading irregularly 

 on either side. Such modes of occurrence seem to indicate a 

 deoxidation of the red slates by imbedded or infiltrating organic 

 matters. 



Mr. Logan had observed that an intrusion of trappeaii rocks 

 at St. Nicolas has altered the shales, and converted them into a 

 material resembling serpentine; and as his researches in the 



* Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 7. No. 45. April 1854. R 



