16 Jt Mr. S. V. Wood on the Form and Distribution of the 



If \vc admit that every elevation takes place at the expense of 

 material removed from subterraneous places to the surface, the 

 void thus caused must, even if we conceive a cavernous structure, 

 be supplied sooner or later by other material subsiding into the 

 cavity, so that in such case we may assume that every volcanic 

 elevation is accompanied by a depression coequal in amount 

 (although perhaps not in area), and also contiguous. Did moun- 

 tain chains come into existence by one great catastrophe, instead 

 of their being formed (as the evidence shows) by a multitude of 

 minor and spasmodic volcanic outbursts, this contiguity would 

 not so necessarily accompany the volcanic elevations; but the 

 smallness of the effect produced by each volcanic elevation when 

 compared with the sum of their action, as seen in mountain 

 chains, shows that, upon the principle stated above, the depres- 

 sions are contiguous. Thus, as it seems to me, every volcanic 

 outburst has a tendency, by the contiguous depressions that it 

 causes, to bring the drainage into its neighbourhood. This 

 drainage is generally the ocean ; but, as in the Caspian, it may 

 be only waters having their origin from the surrounding land 

 collected into the depressed area. And hence is it that great 

 waters are not only contiguous to volcanoes at the present day, 

 but that in all geological periods volcanic outbursts are associated 

 with marine formations. 



Section 2. — The General Geographical Configuration of the 

 Secondary Period. 



The volcanic forces which prevailed during the later part of 

 the palaeozoic period, at least during the carboniferous age, appear 

 to have had a general direction from east to west. The convul- 

 sions which broke up the palaeozoic deposits, and formed the 

 mountain systems which governed the geographical configuration 

 of the secondary period, have obliterated these features to a 

 greater extent than have the tertiary upheavals obliterated those 

 of secondary age; enough, however, remains to show this east 

 and west direction in several well-marked and extensive anticli- 

 nals over the northern hemisphere which originated during the 

 carboniferous period : witness the anticlinals of Nova Scotia, of 

 South Scotland, of North Devon, of the Ardennes, of some of 

 the Sierras of Spain, of Corbieres in the Pyrenees*. The close 

 of this period, however, appears to have been accompanied (or 



* As to Nova Scotia, see Dawson, Proc. Geol. Soc. vol. iv. pp. 184, 269 ; 

 Quart. Journ. Geol. Soc. vol. i. pp. 26,322; vol. iv. p. 50; vol. vi. p. 349 ; 

 vol.viii. p. 398; vol. x. p. 42. As to the Ardennes, see Austen, Quart. 

 Journ. Geol. Soc. vol. xi. p. 533. As to North Devon, Scotland, and 

 Spain, see Murchison's ' Siluria,' London, 1854. As to Corbieres, see 

 D'Archiac, Bull. Soc. Geol. d, France, vol. xiv. p. 507. In addition to which 



