108 R. W. ELLS ON THE GEOLOGY OE 



than the Hudson River formation, although they were from rocks apparently super- 

 imposed. As a consequence of this, the stratigraphical sequence was again studied and 

 the whole area mapped in detail, the result of which was to locate a fault and 

 overthrust, by which the fossiliferous strata of Levis were shoved up by a south-easterly 

 force upon the fossiliferous beds of the Hudson Eivor and Trenton, which latter rested 

 upon the fundamental gneiss of the Laureutian, as seen on the north side of the river at 

 Montmorency and at other points both to the east and west, and that the whole Levis fos- 

 siliferous series was thrown into a great succession of folds. The change of opinion ren- 

 dered necessary by the recent discoveries was speedily announced, and the rocks of the 

 Levis shore, including the limestones, conglomerates and associated graptolitic slates, 

 together w^ith the red and green shale and sandstone series, were transferred from the 

 top of the Hudson River formation to the base of the Low^er Silurian, or the horizon of 

 the Calciferous-Chazy. 



The original view, however, according to which the crystalline rocks of the mountain 

 ranges of the interior were held to be the altered equi^'^alents of those near the river was 

 maintained, though these were now regarded as the equivalents of the altered Calciferous- 

 Chazy rather than of the Hudson River portions of the series ; and to the portion 

 which had now been separated from the general Hudson River formation Logan gave the 

 name of " Quebec Grroup," which name has been retained to the present day. This was 

 in 186L This group was divided into two parts, viz., the Levis and the Sillery, the former 

 comprising the highly fossiliferous slates and conglomerates of Point Levis, whence the 

 name, while the latter was held to embrace the red and green slates and sandstones 

 which, from being well exposed at the village of Sillery, about three miles south of Que- 

 bec, was given the name of that locality. A third division, supposed to be intermediate 

 in position between these and comprising the red and green shales, with certain other 

 beds of the Levis formation, well seen in the seigniory of Lauzon, south of Point Levis, 

 was established and styled Lauzon from the place where first carefully studied. This 

 was first described in the report for 1866. The details of these several divisions will be 

 found stated at length in the ' Geology of Canada,' 1863, and in the report just men- 

 tioned, and it is unnecessary to repeat them here. The order of sequence was Supposed 

 to be upward from the Levis, through the Lauzon, into the Sillery, which w^as regarded 

 for the time being, though this was not clearly established, to constitute the upper mem- 

 ber of the group. Of these three divisions the Levis, as already stated, was highly 

 fossiliferous ; the Lauzon was characterized by the presence of three known species, viz., 

 two lingulœ and an obolella, while the Sillery, which w^as regarded as composed princi- 

 pally of the heavy green-grey sandstones, was not known to be fossiliferous at all. All 

 these formations were regarded as newer than the Potsdam. 



In 1868-69, however, Mr. James Richardson made a somewhat detailed examination 

 of the formations along the south side of the St. Lawrence, from the Chaudière River to 

 Rivière du Loup, and came to the conclusion that certain portions, more particularly 

 including the large areas of whitish quartzose sandstone and associated limestone con- 

 glomerate, should be separated from the position they had so long held and assigned to a 

 lower horizon. He therefore described these portions as belonging to the Potsdam for- 

 mation, and divided them into upper, middle and lower. The cause of the separation 

 was the finding of certain somewhat obscure fossils of supposed primordial age, among 



