1GG Mr. S. V. Wood on the Form and Distribution of the 



structure, however, we know nothing beyond the direction of 

 their strike, will, when examined, present similar evidences of an 

 origin at the close of the palaeozoic period. 



The way in which the secondary formations occur upon the 

 flanks of these known systems, stretching from them in success- 

 ive outcrops, indicate that throughout the secondary period the 

 tracts falling within the influence of these volcanic bands were, 

 with some interruption, undergoing a steady continuous eleva- 

 tion. Thus, to commence on the east with the Oural Mountains, 

 we see that the elevatory action of that chain commenced after 

 the close of the carboniferous period, but was in full action during 

 the last age of the palaeozoic period, the Permian, the deposits of 

 which spread over large tracts, and that this action, prolonged 

 into the secondary period, elevated the Permian deposits into 

 ridges subordinate to the original ridge of the Oural but parallel 

 with it, while the Jurassic deposits were formed in the same but 

 diminished basin as that occupied by the Permian Sea, these 

 now lying within the Permian deposits in a concentric form, 

 precisely as we see the secondary deposits of England and 

 Prance forming successive concentric rings of outcrop diminish- 

 ing in the direct ratio of their age. The system of England and 

 Portugal, although not so marked as the uninterrupted chain of 

 the Oural, is yet distinctly apparent from a consideration of the 

 manner in which the secondary deposits in those countries are 

 assembled. The chief part of the Portuguese system appears 

 now to have disappeared under the Atlantic ; but the Jurassic 

 and subcretaceous deposits which, fenced on the east by the 

 schistose region of Eastern Portugal and Western Spain, oc- 

 cupy the littoral region of Central Portugal, have been shown 

 by the late Mr. Sharpe* to have a regular outcrop along a line 

 of strike from N. by W. to S. by E., in which the earliest- 

 deposited Jurassic formations were elevated at intervals into 

 ridges having this direction until the cretaceous age ; while in 

 England we find this line of the Portuguese strike traversing the 

 island, and becoming conspicuous in the midland and northern 

 counties of England, the volcanic outbursts appearing in the 

 trappean beds of Skye, which there alternate with oolitic depo- 

 sits. The elevatory effect of this band upon the formations of 

 the great secondary gulf of England and Northern France I 

 have before alluded to, in the concentric outcrop of the forma- 

 tions deposited in that gulf, which, like the Oural region and 

 the secondary tract of Portugal, exhibit a gradual and successive 

 elevation and desiccation of the sea-bottom during the whole 

 period, at least until the cretaceous epoch. 



Passing westward, we find under the Atlantic, within the 

 * Quart. Journ. Geol. Soc. vol. vi. p. 135. 



