It. D. Irving — Is there a Huronian Orotcp ? 209 



such cases recalling strongly many regions of later horizontal 

 strata, for instance that of the upper Mississippi valley. 



According to Murray and Logan* — for whose painstaking 

 accuracy and general geological insight I acquired the greatest 

 respect while passing over the region, with their map and 

 descriptions in hand — the series is made up of the following 

 succession of strata, in ascending order, viz :f 



Fig. 1. Section of the original or type Huronian, showing its relation to the 

 pre-Huronian crystallines, Lake Huron. Scale, 10 miles to the inch. Reduced 

 from Logan's section, a-b, Laurentian ; 6-c, Huronian ; d, Cambrian and Lower 

 Silurian. 



Thickness in feet. 



1. Gray quartzite 500 



2. " Chloritic and epidotic slates interstratified with trap- 



like beds " 1 . 2000 



3. White quartzite, often conglomeratic 1000 



4. " Slate-conglomerate, composed of pebbles of gneiss and 



syenite, held in an argillaceous cement of a gray to 

 greenish color " 1280 



5. Limestone, thin-banded, often argillaceous. 300 



6. " Slate-conglomerate," like No. 4 3000 



7. Red quartzite 2300 



8. "Red jasper-conglomerate;" a quartzite with frequent 



red jasper pebbles 2150 



9. White quartzite... 2970 



10. Yellow chert and limestone 400 



11. White quartzite 1500 



12. Yellow chert and impure limestone 200 



13. White quartzite 400 



Total 18,000 



* In the discussion which followed the reading of this paper, the point was 

 made that I gave too much credit to Logan and too little to Murray, in the matter 

 of the working out of the original or type Huronian series. My wish, of course, 

 is to do exactly right in such a matter ; but it is very difficult for one not fami- 

 liar with the inside history of the Canadian Survey, particularly after the lapse of 

 so many years, to adjust the credits correctly. In the Geology of Canada of 1863, 

 which must serve as the source of information, the description of the series is all 

 in Logan's own words, plainly. He also speaks distinctly of having examined 

 this region in person (Preface, p. v) ; while Mr. Murray's examinations are said, 

 in a general way only, to have extended over " Western Canada." In the atlas 

 accompanying the Geology of Canada, however, it is said that the detailed map 

 of the Huronian (Plate III, of the Atlas), to which reference is made above, is 

 " chiefly from the surveys of Mr. Alex. Murray." The sections accompanying 

 this map were drawn by Logan himself. (See Preface to Atlas, p. iv.) It would 

 seem that Logan, after examining the ground himself to some extent, made use of 

 Murray's more detailed studies also, from which to construct the map and sections 

 himself, and to prepare the general description. 



f Abbreviated from Logan's detailed section given in the Geology of Canada, 

 1863, pp. 56-58. 



Am. Jour. Sci.— Third Series, Vol. XXXIV, No. 201.— Sept., 1887. 

 14 



