31-4 On the Oldest FosifUiferuas Deposits. 



where to explain the grounds which we have for inferring that 

 crystulline formations have been elaborated at many successive 

 periods, both secondary, tertiary, and still more modern. We 

 need go no farther, indeed, than the valley of the St Law- 

 rence, now under consideration, to find wide areas covered with 

 marine shells of recent species, at the height of 500 feet above 

 the sea, and where all the rocks can be shewn both to have 

 sunk and to have been again uplifted bodily, for a height and 

 depth of many hundred feet, since the deposition of these shells. 

 But hoAvever firmly we may be convinced that subterranean 

 causes, connected with the development of internal heat, have 

 operated with great, and perhaps nearly uniform intensity, 

 at each successive geological period of equal duration, we 

 must still be prepared to find that by far the largest portions of 

 the visible hypogene rocks are of high relative antiquity to the 

 fossiliferous deposits. This must happen if we are correct in 

 assuming that the crystalline rocks, Avhether stratified or un- 

 stratified, have been formed originally at considerable depths 

 in the crust of the earth. For, in that case, a long period of 

 time must have elapsed after their origin before they can have 

 been brought up within the sphere of human observation. 

 There must have been great upheaval and denudation to cause 

 them to emerge, even in a single district ; but it must require 

 a series of geological epochs before those formed at a given 

 era of the past, can have become generally exposed at the sur- 

 face. A repetition of one series of elevatory movements after 

 another must have taken place in different areas, accompanied 

 by denudation ; and while such forces are acting the deposition 

 of new strata is going on, and the pre-existing crystalline rocks 

 are becoming relatively more and more ancient. 



What was before said, of the succession of ages required to 

 raise deep new formations extensively to the surface (see p. 55) 

 is equally applicable to rocks of deep subterranean origin. 

 Hence it follows that the high relative antiquity of the visible 

 crystalline rocks afford no better a presumption in favour of 

 a period Avhen nothing but granite and gneiss were formed, 

 than the pelagic character of the visible silurian strata and the 

 absence of contemporaneous littoral deposits, simply the uni- 

 versality of the ancient ocean. — Travels in North America, 

 vol. ii. p. 128. 



