the Coralline Crag at Sudboum and Gedgrave near Orford. 323 



where it has been denuded, is a deposit composed ahnost entirely 

 of shells and their debris ; while in the upper portion shells are 

 rarely to be obtained, and only in the valleys corresponding 

 with the present watersheds can this lower stratum be seen. 

 The upper or coraUine portion has here become somewhat indu- 

 rated, and on some occasions has been employed as a building 

 stone, the tower of Chillesford Church having been constructed 

 principally of that material. 



These chimney pipes appear to have perforated the entire 

 thickness of the coralhne crag deposit, at least it is so presumed, 

 although I was unable to ti-ace them to a greater depth than 

 12 or 14 feet from the surface, or immediately beneath the gravel 

 to where they are lost in the talus at the bottom of the pit ; 

 but the crag at these localities has not probably more than 

 20 feet of thickness, as the water stands in the pit at that 

 depth, indicating the presence of the clay beneath. 



The most perfect of these tubes now remaining is one that 

 presents rather more than a semicylindrical shape, but is emptied 

 of its contents by the loss of the lateral supports : a small por- 

 tion of another, the walls of which are as flat and nearly as 

 smooth as the walls of a room, has been undermined so as to be 

 visible from beneath; and through this aperture, which has a dia- 

 meter of about 18 or 20 inches, a boy might readily pass. The 

 large masses of Fascicularia and Theonoa, which in the ordinaiy 

 surface of the crag stand out in prominent relief, were in these 

 chimney pipes literally cut in halves, as if they had been pro- 

 duced by the mechanical operation of a boring implement. 



From the cylindrical form of most of these tubes and their 

 vertical position it is presumed they cannot be ranged in the 

 second class, as it is quite impossible they can have been produced 

 by running water ; and their perfect regularity precludes any inti- 

 mate connexion with the funnel-shaped pipes from the downward 

 action of acidulated waters so removing the carbonate of lime, 

 as in that case they must necessarily have an irregulai- outline. 

 So large a number of them within so small an area militates 

 against the probability of their having been produced by human 

 agency, which the sight of a solitary one might have led to the 

 belief ; their great proximity would have rendered the repetition 

 of such an operation useless, or at least very improbable, and 

 the form of one of them being somewhat elliptical is an evidence 

 against the probability of such a production. 



That the erosion is effected by chemical action, and not bj 

 mechanical means, there is every reason to believe from the regu- 

 larity of form and perfect smoothness of the sides of tl\^se cylin- 

 ders ; for in a mass of deposit composed of a homogeneous 

 material, or nearly so, as regards its chemical components, 



Z2 



