266 DR. THOMAS STERRY HUNT ON THE 
Graywacke—called by him Upper Taconic—to the New York paleozoic system, were, as 
we have seen, adopted in 1861, by the officers of the geological survey of Canada ; who 
then gave to the Graywacke-series the name of the Quebec group, and maintained, on 
paleontological grounds, that it might also represent the Chazy limestone, and thus cor- 
respond to the period between the Trenton limestone and the Potsdam sandstone. It was 
evident that these great differences of thickness, and in lithological characters, between 
the equivalent rocks in the two areas above referred to, must have been the result of, 
widely unlike geographical conditions in the adjacent regions. Along the eastern border 

of the Cambrian sea, great subsidence, and frequent changes permitted the deposition of 
a series of sediments variously estimated at from 10,000 to 25,000 feet in thickness, pre- 
senting an abundant and diversified fauna, with great variations in mineral character, 
often due in part to the materials derived from the contiguous Huronian, Montalban and 
Taconian rocks. 
§129. Meanwhile, it is apparent that over the more stable areas to the westward, along 
the base of the Adirondacks, and between these mountains and the Laurentides to the 
north, there was, during a great part of the period, dry land; and subsequently a region of 
shallow water, in which the only sediments were the silicious sands derived from the 
adjacent Laurentian, or perhaps Taconian rocks; giving rise to the Potsdam sandstone, with 
its ripple-marks, its tracks of crustaceans, and its very scanty fauna, To this succeeded 
lagoons, in which were deposited the dolomites of the so-called Calciferous sand-rock, 
holdiug bitterns, and occasionally gypsum. This deposit rests, in some parts, on the sand- 
stone, and in others directly upon the ancient gneiss. The united thickness of the infra- 
Trenton members of the Champlain division in this region, including the Chazy lime- 
stone, to be mentioned below, will not exceed 1000 feet, and is generally much less. The 
time occupied in their deposition, however, doubtless represented but small portions of the 
long period during which was built up the great Cambrian Graywacke series in the more 
eastern region. The so-called Lower Potsdam beds of the latter, from Troy to Newfound- 
land, not to mention the probably still more ancient Menevian (Paradoxides) beds of 
eastern Massachusetts, southern New Brunswick and Newfoundland—are supposed by 
paleontologists to mark an earlier period than the typical Potsdam of the Champlain and 
Ottawa basins. The fauna of the Levis limestone, which was Eaton’s Sparry lime-rock, 
according to Billings, (who rightly regarded it as the summit of the Quebec group) 
belongs to a horizon superior to that of the typical Calciferous sand-rock. From all of these 
facts we conclude that the original Potsdam and Calciferous sub-divisions are but local 
and partial representatives, alike chronologically and paleontologically, of the great 
Jambrian Graywacke period, anterior to the time of the deposition of the Ordovician 
(Trenton) limestones. 
$130. The fauna of the intermediate and non-magnesian Chazy limestone, as has 
been shown by Billings, serves to connect that of the Levis limestone with the fauna 
of the Trenton. This Chazy limestone is absent in some localities in central New York, 
where, according to Hall, the Trenton rests directly upon the Calciferous, as it does 
elsewhere upon the Cambrian rocks. The deposition of the Chazy in the Ottawa valley is 
distinctly marked as a period of disturbance, since it presents at its base a limestone-con- 
glomerate, resting on the Calciferous, and followed by about fifty feet of sandstones and 
shales ; to which succeed the fossiliferous beds of pure limestone, sometimes with dolomitic 

