208 i?. D. Irving — Is there a Huronian Group f 



all information to date. "With this description he gives also a 

 detailed map and sections of " The Huronian Bocks" on the 

 north shore of Lake Huron, between the St. Mary's and Mis- 

 sissagui rivers. This particular series Murray had described 

 as early as 1848, as "a set of regularly stratified masses, con- 

 sisting of quartz rocks or altered sandstones, conglomerates, 

 slates and limestones, interstratified with beds of greenstone." 

 Although both Logan and Murray extended the name Huron- 

 ian to other rocks in the Lake Superior region this series was 

 the only one so covered that was ever studied and mapped in 

 any thorough mariner, while the correlation of the other so- 

 called Huronian areas with this one rested always on a pretty 

 slender foundation. If then we seek — as we must do — for a 

 type series with which to start a study of the so-called Huron- 

 ian, we can find it only in this Lake Huron Series. This seems 

 indeed to have done duty more or less definitely as such a type 

 in the writings of European and American geologists for five 

 and twenty years ; although, most unfortunately, of the many 

 who have made use of the name Huronian, only a very few 

 have studied these rocks on the ground, in any such manner as 

 to warrant the opinions they have so freely expressed. 



Evidently our inquiry should begin with a study of this type 

 series of rocks. Is this series, in its nature, volume and sub- 

 ordinate divisions, entitled to the rank of a clastic group? Do 

 its structural relations and lithological contrasts with the great 

 mass of the ArchEean, with which it is in direct contact, indi- 

 cate a chronological separateness? In attempting an answer to 

 these questions, I make use not only of the facts summarized in 

 Logan's descriptions and upon his map, but also of the results 

 of my own observations extended during two seasons, not only 

 in the area especially mapped as Huronian on the plate to 

 which I have already referred, but also over a large contiguous 

 area further to the eastward, which has been mapped as Huro- 

 nian on the recent general maps of the Canadian Survey. 



III. Briefly, then, that series of rocks, which is especially 

 mapped by Logan on the plate above referred to, and which 

 we may properly designate as the type or original Huronian, 

 may be described as a great succession of quartzite layers, 

 including a subordinate quantity of greywackes, a much smaller 

 proportion of "limestone and chert" and numerous eruptive 

 diabasic greenstones ; the latter occurring both in dyke and 

 sheet form. In the main the series is but very gently bowed. 

 Only rarely the inclinations of the strata reach twenty degrees, 

 while large areas occur, particularly in the interior and away 

 from the lake shore, where the strata are not visibly removed 

 from horizontality, the whole appearance of the topography in 



