the Coralline Crag at Sudbourn and Gedgrave near Orford. 325 



duction of tliese gases must be accounted for, either by the sup- 

 position of their having risen from regions of considerable depth 

 through the clay out of rocks of an igneous character beneath, 

 or that some acid gas may have been formed in the clay itself by 

 the decomposition of pyrites which is found in great abundance 

 in that deposit ; in either case it would be necessary, I should 

 imagine, for cavities to have existed in the clay either for the 

 passage of the gas or for its elaboration ; and although no ap- 

 pearance exists of anything like disturbance in this neighbour- 

 hood, it may be remembered that the sea now approaches within 

 a mile of the locus in quo, and all traces of such action may have 

 been removed. 



In speaking of the "sand-pipes" of the chalk. Sir Charles Lyell 

 says, " If some of the largest pipes, of which the bottom has not 

 been yet reached, be prolonged indefinitely downwards and con- 

 nected with deep fissures, we may suppose that springs charged 

 with carbonic acid rose up at some former period through the 

 chalk and crag while these were still submerged. In proportion as 

 the chalk was corroded, the incumbent substances wou.ld subside 

 into the hollows thus formed, and the water would freely perco- 

 late, the matter thus intruding itself dissolving any calcareous 

 ingredients which may be associated with it, and still continuing 

 to widen the tube by corroding its walls." 



Our chimney pipes were probably formed, as above stated, 

 while the crag was beneath the sea, although I was unable to 

 ascertain what were the true contents of these openings when 

 first broken into. The form of one of these being of a funnel 

 shape and opening outwards, would seem rather to imply a dif- 

 ferent mode of action from the other moj-e perfectly formed 

 cylinders in close proximity, bearing in that character a resem- 

 blance to the funnel-pipes of the general surface. I am inclined, 

 however, to believe this tube is continued downwards, of a 

 cylindrical form, and produced in the same manner, the enlarge- 

 ment of the upper part having been caused by some impediment 

 to the ready and regular escape of the gas, retaining it near the 

 surface, where it has in consequence exerted a more destructive 

 force, the erosive power diminishing downwards, causing the 

 angular inclination of the sides. 



These pipes seem to differ from those of the Geysers in Iceland, 

 or others that have been formed by water in various parts of the 

 world in the immediate neighbourhood of volcanoes, inasmuch as 

 from the fragile nature of the crag rock, the narrow partition 

 between these pipes would have been ruptured by the upward 

 action of water impelled through them with any degree of vio- 

 lence ; and the more probable solution appears to be the quiet 

 action of carbonic acid gas evolved in an iipward direction ; and 



