1^8 KEPORT 1856. 



Looking at the conditions under which strata repose upon each other, we may view 

 their relations of superposition under the four following categories. 



1st. Successive deposits may lie together in parallel arrangement, and so graduate 

 into each other as to denote no pause in time or interruption in the formative process ; 

 and even a formation of one long period may thus graduate into another by their 

 sediments and their fossils. Such a close following of strata, the author entitles a 

 conformable continuous sequence. 



2nd. One set of strata may rest immediately on another with perfect parallelism, 

 and yet their plane of contact represent a long interval of time and a total change of 

 sedimentary conditions and of the physical geography ; for certain beds or even whole 

 formations interposed between them in other districts, may be altogether absent. 

 This relationship is entitled a conformaUe interrtipted sequence. 



It proves not merely a lift of the w^atery floor into dry land, and its subsequent 

 re-immersion, but a movement unaccompanied by any tilting or undulation of the 

 lower deposit. 



3rd. An upper group of beds may repose on a lower with an angle between them 

 such as to imply an uptilting from horizontality in the inferior, before the superior 

 was deposited, while a close sequence of type in their organic remains shows them to 

 be the products of immediately consecutive periods, or that no time elapsed for the 

 production elsewhere of a middle formation. This relationship is entitled an uncon- 

 formable continuous sequence. 



4th. Two sets of strata resting in contact, may present not only an absence of 

 parallellism, but an omission of one or more intermediate formations elsewhere 

 existing. This state of things implies not only an inclining of the inferior beds, but a 

 lifting of them into dry land, with a lapse of time before their imraersionfor the recep- 

 tion of the overlying deposits. Such a condition, familiar as the commonest species of 

 unconformity, may fitly be entitled an unconformable interrupted sequence. 



The fifteen principal divisions of the Appalachian palaeozoic strata contain several 

 important planes of discontinuity. These are of very unequal magnitude, both geogra- 

 phically and stratigraphically. Between them are other lesser horizons, but only the 

 greater'ones are discussed in this paper. The two most conspicuous of all, are that 

 at the end of the Matinal or Hudson River period, and that at the beginning of the 

 Vespertine or first Carboniferous age. Another, though materially less extensive 

 one, divides the Premeridian or Lower Helderberg period from the Meridian or 

 Oriskany sandstone age. 



Evidences of an extensive Paroxysmal Revolution in the Physical Geography and 

 Organic Inhabitants of the Appalachian Sea at the end of the Matinal Period. 

 The break or plane of discontinuity terminating the Matinal series or Hudson 

 River group, exceeds all the others in the Appalachian basin for the abruptness of 

 the transition which it implies in the organic remains, and in the magnitude of the 

 crust-movement. From the Gulf of St. Lawrence to the Hudson River, nearly 800 

 miles, this break is marked by an unconformable interrupted sequence ; the Matinal 

 rocks highly inclined and folded, generally supporting less inclined strata of the Levant 

 or some other middle paleeozoic formation. The Scalent or Niagara group, next to ' 

 the highest of the four true Silurian equivalents, reposes discordantly upon the Upper 

 Cambrian or Matinal, not only in the Peninsula of Gaspe, but in the Eastern Town- 

 ships and in Vermont. The evidence of a great crust-movement at this epoch of the 

 close of the Matinal slates, was shown by the author as long ago as 1838, in an 

 annual report on the geological survey of Pennsylvania, where he pointed out the 

 unconformity in the vicinity of the Hudson River, and drew the inference of an up- 

 heaval of the bed of the ancient ocean. It would appear that throughout this north- 

 eastern division of the Appalachian chain, the movement at the epoch separating the 

 Cambrian and Silurian or older and newer Silurian periods, was so vehement, as to 

 plicate and partially metamorphose the older strata. The condition of unconformity, 

 with and without interruption of sequence in the strata, extends to the west side of 

 the River Hudson, and there is good geological evidence that the displacement of level 

 producing it reached westward as far as Oneida Lake. Undulated Matinal rocks 

 support horizontal Niagara or Scalent strata, with a lapse of two intermediate for- 

 mations for some distance from the Hudson, westward along the base of the Helderberg 



