THK HUUOMAN ffj ~IKM. 



noticed in the last chapter has however, among other important results, 

 enabled Professor Bailey and his able coadjutors to introduce into his 

 " Observations on the Geology of New Brunswick" the two great 

 groups of rocks which stand at the head of this chapter, while Mr 

 Murray has recognised the Laurentian in Newfoundland, and a con- 

 siderable area on the banks of the Lower Hudson has also been referred 

 to the same period. These discoveries indicate a second long line of 

 outcrop of Laurentian rocks parallel to that previously known-, and 

 separated from it by broad areas of Silurian, Devonian, and Carbon- 

 iferous rocks. They also show that immediately after the Laurentian 

 period, not only the breadth of the American continent in the north 

 was marked out by these rocks, but also the direction of its eastern 

 coast. 



Hurunian Series [Coldbrook Group). 



Under the St John or Acadian series, in the vicinity of St John, 

 and more especially at Coldbrook, there occurs a group of unevenly 

 bedded rocks, evidently marking a period of much disturbance, and 

 consisting, in large part, of conglomerate and of beds which seem to 

 be of the character of volcanic tufa or indurated volcanic ash. In 

 mineral character these beds closely resemble the Huronian of 

 Georgian Bay, and as they underlie the Primordial slates of St John, 

 I think we are fully justified in assigning them to this age. Should 

 this view prove correct, the occurrence of these peculiar beds in New 

 Brunswick, and also in the basin of the great Canadian lakes, will 

 constitute an interesting illustration of the existence of similar physical 

 conditions at the same time in widely separated areas, and will 

 increase our appreciation of the geological importance of that period 

 of physical disturbance which seems to have separated the quiet seas 

 of the Laurentian with their reefs of Eozoon from the equally quiet 

 conditions of the Lower Silurian ocean. 



Though visible only along a line of outcrop about thirty miles in 

 length, and a few miles wide, these Huronian beds attain in one 

 locality, according to Mr Matthew, a vertical thickness of not less 

 than 7000 feet. In other places, however, their thickness is stated to 

 be only 150 feet. On this difference of thickness, and the composi- 

 tion of the group, Mr Matthew bases the following remarks: — 



" These figures indicate that the ancient continent, previously ele- 

 vated above the sea, sank under the accumulated weight of Huronian 

 sediment to the extent of one mile and a half or more in that short 

 distance, and that a coast-line near the position now occupied by the 

 city of St John limited the Huronian sea to the eastward during a 

 great part of this period. 



