R. D. Irving — Is there a Huronian Group ? 215 



upon these and filling the irregularities of the original surface, 

 the conglomerate rock, which dips some thirty degrees toward 

 the northwest. The stratiform arrangement of the conglom- 

 erate is finely brought out by the interleaving of sandy layers, 

 in which the pebbles are wanting, or nearly so. The sub-angu- 

 lar to angular fragments of the conglomerate, ranging in size 

 from a fine detritus to bowlders two feet in length, are confus- 

 edly heaped together in the vicinity of "the immediate contact; 

 but further away show a tendency to arrangement in bands. 

 They are mainly composed, in order of relative abundance, of 

 a gray biotite gneiss or gneissoid granite, of red granite (inclu- 

 ding several varieties) and of dark-colored schists. The matrix, 

 which is at times almost or wholly excluded by the bowlders, is 

 mainly a fine detritus of the same nature as the fragments, 

 the constituent minerals of the original rocks becoming more 

 thoroughly separated from one another as the particles are 

 finer. This finer detritus becomes more quartzose and arena- 

 ceous in the interleaved, non-conglomeratic layers, particularly 

 as one passes away from the immediate contact. In these por- 

 tions also there is present more or less of a kaolinic or sericitic 

 ingredient resulting from the decay of the feldspathic consti- 

 tuents. Finally, invading the matrix very irregularly, at times 

 giving it the appearance of a completely vitreous quartzite, and 

 again leaving it very arenaceous in texture, is a siliceous 

 cement, which has partly separated out as a finely interlocking 

 quartz but often has divided itself off more or less thoroughly 

 as enlargements of the quartz fragments. Upwards the con- 

 glomerate graduates into an arenaceous quartzite. 



Closely analogous phenomena are to be seen at the contacts 

 of these two sets of rocks displayed at three points on the line 

 of that branch of the Canadian Pacific which runs from Algoma 

 Mills to Sudbury on the main line, and particularly in the 

 vicinity of the mouth of Serpent River. The pebbles and 

 bowlders at these contacts are of all sizes up to two or three 

 feet in diameter, and include granite, gneiss and mica-schist. 

 It should be added that fragments of gneiss and granite are met 

 with at various horizons through the Huronian series, often in 

 considerable abundance in one place, while large parts of the 

 series are composed of a little assorted granitic and gneissic de- 

 tritus. These pebbles, and the finer gneissic detritus, though 

 not at the base of the series, furnish strong evidence of the 

 relatively great antiquity of the rocks which yielded them. 



Thus the structural relations of the original or typical 

 Huronian series to the older schists are such as to render abun- 

 dantly evident its entire chronological separateness from them ; 

 and the second part also of our inquiry is answered in the 

 affirmative. 



