314 



PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



One of the most remarkable phenomena in this "pit is to be ob- 

 served on its southern side. A cylindrical pipe (e), of small 

 diameter, divides into two smaller cylinders, two or three inches 

 in diameter each. They are separated one from the other by an 

 interval of 2 or 3 inches, and each holds an uninterrupted course 

 through the chalk to the depth of several feet. In this and in 

 other instances of the same kind that I have met with in Norfolk, 

 the division of the pipe into two branches appeared to have been 

 caused by a flint obstructing nearly the whole area of the pipe » 



Fig. 13. 

 South side. 



Chalk, rubble, and Chalk. 



Lowest line of Flints. 



Overlying sand. 



on 



&tcS=&Ct .&3<&$9d 



Floor of the pit. 



and- the diameters of the smaller cylinders into which it divided 

 appeared to be influenced by the size of the apertures left in the 

 mass of flint. 



In another pipe on the east side of the Crostwick pit, a flint (/), 

 is seen, one part of which remains imbedded in the chalk, while 

 the other part projects into the cavity of the pipe. The upper 

 surface of the projecting part has indications of wear, while its 

 under surface retains the original chalky coating. 



In another part of the same pit I observed fissures radiating 

 from one of the pipes ; and these fissures were filled with the same 

 fine clay with which the pipes are usually lined. I have since met 

 with similar fissures, similarly lined, in pipes traversing the solid 

 chalk : they occur in pits in this part of Norfolk. 



In a paper on the detrital deposits of part of West Norfolk, 

 (Proceedings of the Geol. Soc. vol. iii. p. 185.), I showed that the 

 chalk is there covered by two deposits of very variable thickness. 

 The upper consists of ferruginous sand or loam, and of numerous 

 chalk flints, which have undergone scarcely any abrasion, together 

 with a few fragments of other rocks, such as trap, porphyry, &c, 

 which indicate distant transport : and with these ingredients, beds 

 of rolled chalk-pebbles are occasionally associated. The lower 

 deposit consists mainly of fragmentary chalk, which has undergone 



