274 T. S. Hunt—History of Pre-Cambrian Rocks 
brook was explained by supposing both groups to consist in 
large part of volcanic rocks. 
In 1869 and 1870, however, the writer, in company with the 
gentlemen just named, devoted many weeks to a careful study 
of these rocks in southern New Brunswick, when it was made 
apparent that the Bloomsbury groap was but a repetition of 
the Coldbrook on the opposite side of a closely folded synclinal 
holding Menevian sediments. These two areas of pre-Cambrian 
rocks were accordingly described by Messrs. Matthews and 
Bailey in their report to the geological survey of Canada in 
1871, as Huronian, in which were also included the similar 
erystalline rocks belonging to two other areas, which had been 
previously described by the same observers under the names of 
the Kingston and Coastal groups, and by them regarded as 
n close association with these Huronian strata in eastern 
Massachusetts is found a great development of petrosilex rocks, 
ignated by Matthews and Bailey, feldspathic quartzites < 
siliceous and porphyritic slates, which form the chief part 0 
in New Brunswick. The petrosilexes of dome hile 
im 
1870, and in 1871, as indigenous stratified rocks forming a part 
of the Huronian series. He subsequently, in 1871, studied the 
similar rocks in southeastern Missouri, and, in 1872, 02 the 
north shore of Lake Superior, but was unable to find them ™ 
the Green Mountain belt, or in its southward continuation, 
until, in 1875, he detected them occupying a considerable are 
