TRANSACTIONS OF THE SECTIONS. 181 



fringe it were accumulated. It seems not to have been sensibly upheaved since the 

 date of their deposition. 



Of the age of the palaeozoic basin of Hudson Bay, recent research has furnished 

 some very suggestive information. According to the statements of the geologists of the 

 Canadian government, and others, it has hitherto disclosed not a single fossil indi- 

 cative of the existence of either the Primal, Auroral, or Matinal formations of the 

 older palaeozoic series, but it abounds in deposits of middle palaeozoic or Silurian 

 age. Mr. Isbister, in an admirable summary of the results of research in this region, 

 considers this important general fact to be well-established for all the widely scattered 

 localities hitherto visited. It receives the strongest confirmation from the determi- 

 nations of Mr. Salter, who has devoted a careful scrutiny to the extensive collection 

 of fossils brought to England by the recent Arctic expeditions. According to Isbister, 

 middle palaeozoic or Silurian rocks extend uninterruptedly from Lake Temiscaming, 

 a little above 47° latitude, to the shores of Wellington Channel beyond ^7°, or through 

 more than 30°. From all the geological evidence collected, it would appear that a 

 large portion, if not the whole of this wide palaeozoic area remained uncovered by 

 the sea throughout the three earlier or Cambrian periods, and was not submersed 

 until that stupendous disturbance of the crust took place which displaced so large a 

 tract of the bed of the Appalachian ocean. This north-eastern area was therefore 

 the nucleus of the continent, or, at least, one island centre, from the infancy of its 

 growth down to the end of the Matinal ages. The stupendous movement which 

 then depressed its central districts, converting it into a Silurian basin, also lifted off 

 a large part of the waters to the south of the neutral axis of motion marked by the 

 dividing zone of metamorphic strata. No sharp corrugations of the crust attended 

 this enormous displacement of the levels, analogous to the crust-undulations of the 

 same epoch between Gaspe and the Hudson. Still the subsidence of the Hudson 

 Bay region must have been violent or paroxysmal, if we are to judge from the con- 

 glomerates which strew its immediate floor, their lowest bed, according to Sir William 

 Logan, being composed of great boulders and blocks of sandstone, some of them 9 feet 

 in diameter, so energetic was the disturbance which attended the letting on of the 

 waters. It is not certain that this subsidence occurred at the beginning of the 

 Levant or first Silurian period, for Mr. Salter has shown* that all the strata of the 

 southern border of the Hudson Bay area yet examined, are of the age of the Scalent 

 or Niagara limestone. It is probable that after the first tremendous and nearly 

 universal disturbance of the levels at the close of the Matinal period, there occurred 

 an interval of comparative repose, with a slow deposition of the Levant and Surgent 

 formations in the central and southern tracts of the Appalachian Sea, and also in the 

 central parts of the Hudson Bay basin; and that succeeding this there was a broad, 

 nearly equalized subsidence of the whole northern basin, and the northern half of the 

 southern one in the Scalent or Niagara period. 



Reviewing all the facts, it would seem that the wide break in the sequence of the 

 American palaeozoic strata above the Matinal, or latest Cambrian formation, is as 

 well indicated north of the Laurentian metamorphic zone as south of it, though not 

 by a physical unconformity in the usual narrow sense, but by a prodigious hiatus in 

 the series of deposits. 



[The paper next contains " Evidences of a physical break or interruption in the 

 depositions between the Premeridian or latest Silurian, and Pomeridian or Devonian 

 formations," and also " Evidences of a similar physical break between the Pomeri- 

 dian and Vespertine, or earliest Carboniferous formations." These instances of dis- 

 cordant sequence are shown to be of less magnitude than that already discussed 

 between the Matinal and succeeding deposits; and as the physical breaks are, so are 

 the palaeontologic ; the transition in the organic remains being far more complete 

 and abrupt between the lower and middle palaozoics, than between the middle and 

 upper or anywhere within the middle between its Silurian and Devonian equivalents.] 



PalcBontological Break, or Amount of Change in the Organic Remains between the 

 Older and Middle PaltBozoic Strata of the Appalachian Basin. 



Great as the physical discordance is between the lower and middle palaeozoic 

 formations, the palaeontological break or the transition in the fossils is even more re- 

 * Proceedings of British Association, 1851. 



