284 STEATIGRAPHICAL GEOLOGY 



The trough-like syncline in which the limestones lie is a feature 

 produced by subsequent flexuring ; there is no indication of a 

 shore-line either along the northern or the southern line of outcrop, 

 and we have only to prolong the dip of these limestones to see that 

 they must have extended indefinitely both to the northward and 

 to the southward. "Who will deny that there may be another 

 syncline under Holland, and that Carboniferous limestone may 

 occur in it ? 



From the distribution of the limestones, as above indicated, we 

 may infer that no large rivers entered that portion of the Avonian 

 sea which is now Central Ireland, and also that the island tract 

 of St. George's Land had then a dry climate and was without 

 streams of any size. At the same time there is no ground for 

 supposing that the limestones formed around this island were of 

 the nature of coral-reefs. Crinoids and molluscan shells are the 

 predominant constituents of these limestones as they are of the 

 Devonian limestones (see p. 206), and the corals are distributed 

 through the limestones over wide areas, not concentrated in reef- 

 like masses round the shores of the island. 



1 A. Vaughan, Quart, Journ. Geol. Soc. vol. Ixi. p. 181. 



2 "Geology of the S. Wales Coalfield," Mem. Geol. Survey, in ten 

 separate parts. 



3 Hind and Stobbs, Qeol. Mag., 1906, pp. 385, 445, 496. 



4 J. W. Sibly in Quart. Journ. Geol. Soc. vol. Ixiv. p. 34. 

 8 E. J. Garwood, Geol. Mag. for 1907, p. 70. 



6 W. Hind, Quart. Journ. Geol. Soc. vol. Ivii. p. 347. 



7 C. A. Johns in The Naturalist for 1911, p. 9. 



8 E. J. Garwood, Proc. Geol. Soc., May 18, 1911. 



9 E. J. Garwood in "Geology in the Field," Geol. Assoc. (1910), p. 661. 



10 Goodchild, Proc. Geol. Soc. vol. xv. p. 117 (1897). 



11 "Geology of the Country around Edinburgh," M em. Geol. Surv. 2nd 

 ed., 1910. 



12 K. J. Cruise, Mem. Geol. Surv., Ireland, Expl. of Sheets 66 and 67. 



13 J. A. Douglas, Quart. Journ. Geol. Soc. vol. Ixv. p. 538 (1909). 



14 Jukes, Manual of Geology, 2nd ed. p. 512 (1862). 



15 Messrs. Matley and Vaughau, Quart. Journ. Geol. Soc. vol Ixiv. 

 p. 413. 



16 Jukes, op. cit. 2nd ed. p. 510, 3rd ed. p. 588. 



17 Salter, Quart. Journ. Geol. Soc. vol. xix. p. 476 (1863). 



18 W. Hind, Geol. Mag., 1904, pp. 392, 584. 



19 C. Reid in Sum. Prog. Geol. Surv. for 1908, p. 26. 



20 Jukes-Browne, Geol. Mag. 1905, p. 353. 



21 A. Vaughan, Brit. Assoc. Rep. Sect. C. (1910). 



22 Barrois, " Terrains an ciens des Asturies," J/ewi. Soc. Geol. Nord (1882), 

 p. 519. 



