on American Qeology, 91 



although the trilobites recall by their aspect those found by Owen 

 in the Lower Sandstone of the Mississippi. Seven species alone 

 out of this fauna have been identified with those known in other 

 formations, and of these one is Chazy, while six belong to the 

 Calciferous, to which latter horizon Mr. Billings considers the 

 Quebec group to belong. The Chazy has not yet been identified 

 in this region, unless indeed it be represented in some of the upper 

 portions of the Quebec group. The Calciferous sand-rock is want- 

 ing along the north side of the St. Lawrence valley from near 

 Lake St. Peter to the Mingan Islands, but at Lorette behind Que- 

 bec, at the foot of the Laurentides, the Birdseye limestone is 

 found reposing conformably upon the Potsdam sandstone. 



It is not easy to find the exact horizon of the Potsdam sandstone 

 among the black shales which underlie the Quebec group. The 

 JScolithus of Rogers' Primal sandstone, and of the summit of 

 Safford's 3rd or Chilhowee formation is identical with that found 

 in the quartz rock at the western base of the Green Mts, and fig- 

 ured by Mr. Hall in the 1st volume of the Palaeontology. It is 

 however distinct from what has been csWed ScoUthus in the Pots- 

 dam of Canada. The value of this fossil as a means of identifi- 

 cation is diminished bv the fact that similar marks are found in 

 sandstones of very difi"erent ages. Thus a Scolithus very like that 

 of the St. Lawrence valley occurs in the sandstone of Lake 

 Superior and in the Medina sandstone, while in Western Scot- 

 land, according to Mr. Salter, the two quartzite formations above 

 and below the Lower Silurian limestones of Chazy age are alike 

 characterized by these tubular markings, which are regarded by 

 him as produced by annelids or sea-worms. We find however in 

 shales which underlie the Quebec group at Georgia in Vermont, 

 trilobites which were described by Mr. Hall in 1859 as belong- 

 ing to the genus Olenus, a recognized primordial type ; he has 

 since erected them into a new genus. Again at Braintree in Eastern 

 Massachusetts occur the well known Parad oxides in an argilla- 

 ceous slate. These latter fossils Mr. Hall suggests probably belong 

 to the same horizon as certain slaty beds in the Potsdam sand- 

 stone, or perhaps even at the base of this formation. (Introduction, 

 page 9.) In this connection we must recall the similar shales of 

 Newfoundland,in whieh Salter has recognized trilobites of the same 

 genus. These shales containing Faradoxides, like those underlying 

 the Quebec group, thus appear to belong to the so-called Primor- 

 dial zone, and are to be regarded as the equivalents of the Potsdam 



