258 Mr. Lyell on the tMhular Cavities Jilled -with Gravel 



These deep and narrow pipes are very symmetrical at Eaton, 

 having the form of inverted cones, which at their upper ex- 

 tremity vary in width from a few inches to more than four 

 yards, while at their lower they taper down to a fine point : 

 see fig. 1. The smaller ones, which are usually about a foot 



Fig. 1. 



~^_, 



Sand-pipes in the Chalk at Eaton near Norwich. 



in diameter, seldom penetrate to the depth of more than twelve 

 feet, while the larger are sometimes more than sixty feet 

 deep. They are for the most part perpendicular in their di- 

 rection, and nearly circular in shape, although they often ap- 

 pear of an oval form when cut through in the precipices sur- 

 rounding the Eaton quarries, because the plane of intersection 

 is there in reality oblique, and inclined at an angle of about 

 80° with the horizon. Several sand-pipes often approach 

 very near to each other without any tendency to unite. In 

 proof of this general fact, Mr. Ewing pointed out to me three 

 pipes close to each other, which we explored from top to bot- 

 tom by digging. The depth of one proved to be twelve feet, 

 that of another nine feet, and that of the pipe placed between 

 the other two six feet. Although they all came within three 

 or four inches of each other, the parting wall of white soft 

 chalk was in no instance broken through; see a; fig. 1. 



Contents of the Sand-pipes. — The materials filling the sand- 

 pipes are of three kinds: 1st, sand and pebbles; 2ndly, loose 

 unrounded chalk flints; Srdly, fine ochreous sandy clay, not 

 hnpervious to water. The rounded pebbles in the first consist 

 chiefly of black flint, while a small number are of white quartz. 

 With these are sometimes seen unrounded fragments of sand- 

 stone, with a cement of oxide of iron ; the whole agreeing with 

 the contents of the deposit incumbent on the chalk, which at 



