128 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



1. Region North of the Barrier. — South-easterly Attenuation of the Argil- 



laceo-arenaceous Strata. — North-westerly Attenuation of the Calcareous 

 Strata. 

 Distribution of the "Sedimentary" Strata and of the Limestones of the Car- 

 boniferous Period: — 



South Stafibrdshire. Anglesea. 



Warwickshire Coal-field. Notts, Derbysliire, and Yorkshire. 



Leicestershire Coal-field. Lancashire. 



North Staffordshire. Cumberland. 



Flintsliire and Derbyshire. Scotland. 



2. Region South of the Barrier. — Easterly Attenuation of the Argillaceo-arena- 



ceous Strata. — Westerly Attenuation of the Calcareous Strata. 



3. North Atlantic Continent. — Northerly Drift of Sediment dm*ing the Car- 



boniferous and Mesozoic times. 

 III. Summary of Conclusions, 



[Note. — In the following pages the term "Sedimentary" is used to denote 

 exclusively such inorganic strata as sandstones, clay, shales, &c., in opposition to 

 Calcareous strata or limestones.] 



§ 1. — Introduction. — A large and interesting field of inquiry is 

 open to us in comparisons of the relative distribution of the calca- 

 reous and the truly sedimentary members of different geological 

 formations. We have, as it appears to me, been too much in the 

 habit of classing limestones (whether coralline, crinoidal, shelly, 

 or oolitic) as strictly sedimentary ; yet it will be found, by such 

 comparisons as those alluded to, that the relation which is borne 

 by sandstones and shales to limestones is one, not of similarity, but 

 of contrast. In other words, that where we have a group of strata, 

 as, for example, the Lower Carboniferous, composed partly of " sedi- 

 mentary" and partly of calcareous members, it will generally be 

 found that the one series is complemental of the other, and developed 

 from opposite directions. This arises from the differences in the 

 origin of the two classes of stratified rocks, the calcareous being 

 essentially organic, and the " sedimentary " essentially mechanical ; 

 so that where the forces and agencies tending to the accumulation of 

 the latter are in active operation, these very forces and agencies are 

 in direct antagonism to the other, and, as a result, calcareous strata 

 are either not formed or only sparingly*. 



(a.) Of these two ever-acting principles we have numerous ex- 

 amples both in recent and in geologic periods. If we take as an illus- 

 tration the Gulf of Mexico and the West Indian Islands, we find 

 the sediment brought down by the Mississippi forming deposits of 

 sand and clay which are spread along the coast and far out to sea 

 by the Gulf-stream, while around the West Indian Islands coralline 



* That limestones are either directly or indirectly the production of animals 

 is now so generally admitted that it seems scarcely necessary to cite authorities. 

 Bischof in his work on Chemical Geology (vol. iii. p. 35) says, " So long as the 

 formation of mechanical deposits was predominant, the organic action of the 

 marine animals that separate limestone, or at least that of tlie corals, could not 

 be exercised." This passage (which did not come under my notice until these 

 pages had been brought before the Geological Society) fully bears out the prin- 

 ciple of opposition between the origin of the two classes of rocks, which I ani 

 now endeavouring to illustrate. See also Lieut- Nelson's ' Account of the Ber- 

 muda Coral -formations,' Trans. Gaol. Soc. 2nd series, vol. v. 



