170 On Land-tracts during the Secondary and Tertiary Periods. 



other, have observed a remarkable absence, or at least rarity, of 

 volcanic rocks penetrating the pataozoic portion or core of the 

 chains, these rocks being developed in the lateral region where 

 the secondary formations were deposited, — illustrating, I venture 

 to think, the hypothesis mentioned in Section 1, that the con- 

 tiguity of the sea (as shown here by the deposits) to the volcanic 

 foci is due to the depressions caused by the volcanic action, its 

 absence from those parts of the chains deficient in volcanic rocks 

 being due to the steadiness of level there permitted by the absence, 

 during the period, of volcanic disturbances. These two great 

 systems of the Andes and the Rocky Mountains, although origi- 

 nating early in the secondary period, have preserved their aligne- 

 ment and activity until the present time ; for although the Andes 

 be the only one of them in which the volcanic force is still en- 

 tirely active, yet the Rocky Mountains themselves, as well as the 

 Cascade Mountains and the other Pacific-coast ranges (which are 

 but the lateral and subordinate chains of the great Rocky-Moun- 

 tain system), exhibit evidences of very recent volcanic activity*. 



We thus see over half the northern hemisphere, and again in 

 important parts of the southern, well-marked evidences of the 

 continental development which prevailed during the secondary 

 period, sufficient, I think, to justify an inference that during 

 that period, when the chief part of the present Europeo-Asiatic 

 continent and of Northern Africa was sea, the continents had 

 an align ement from north to south as well marked as is the 

 Europeo-Asiatic continent of the present day in the opposite 

 direction (the great development of which from east to west 

 being due, as I shall presently attempt to show, to the east and 

 west development of tertiary volcanic bands), all the examples of 

 great systems of secondary origin yet studied, with the exception 

 of the Jura and of part of the Pyrenees (both of which originated 

 very late in the secondary period), having this north and south di- 

 rection. This inference will be greatly strengthened if further ex- 

 plorations should show that the north and south ridges of Central 

 and Southern Africa, to which the configuration of that conti- 

 nent south of the Niger is due, and the north and south ridges 

 of Madagascar are of contemporaneous origin with those of 

 Australia, the Alleghanies, and the Oural, and contributed to 

 the geographical configuration of the secondary period. In 

 short, it may be asserted that the present configuration of "our 

 continents is due to the engrafting, as it were, upon secondary 

 continents or their remains, of post-cretaceous land, elevated by 

 mountain chains running from west to east which have come 

 into existence since the close of the secondary period, — in some 



* See Geology of California and Oregon, by J. S. Newberry (Wash- 

 ington, 1857). Bauerman, Quart. Journ. Geol. Soc. vol. xvi. p. 198. 



