CLAY-BEARING FORMATIONS. 357 



CLAY MARL III. 



As already indicated (pp. 156, 157) the clay found in this 

 member of the Clay Marl series consists of local deposits sur- 

 rounded by sand. The material is worked at Thackara's brick- 

 yard south of Woodbury (Loc. 155), and it is there rather sandy. 

 It is also exposed at Dobb's old yard a short distance south of 

 Thackara's, where it forms an extremely sticky, dense, plastic 

 clay with the following characters : 



Physical characters of a clay in Clay Marl III. 



Water required for mixing, 4°-5% 



Air shrinkage, 9 % 



C Minimum, 133. 

 Tensile strength, lbs. \ Maximum , ,36. 



P er S( l- in - (Average, 134. 



In burning it behaved as follows : 



Cone. 05. 01. 



Fire shrinkage, 4.3 % 4.6 % 



Absorption, 11.28% 8.76% 



It is doubtful if this clay could be used alone for anything 

 except common pottery, and for brickmaking considerable sand 

 would have to be mixed with it. The test of this single sample, 

 however, cannot be taken as necessarily indicative of the quality 

 of other clay lenses in this formation. 



CLAY MARL II. 



The area of outcrop of Clay Marl II, and its stratigraphic 

 characters have been described (p. 157). On account of the 

 undulating character of the region in which this clay occurs, it 

 is often possible to find exposures along the banks of streams or 

 in road cuttings, from which a knowledge of the character of 

 the material can be obtained. The exposures are often of con- 

 siderable thickness such as fifteen or twenty feet, and when 



