CLAYS. 227 



The blue clay, which is of Pleistocene age, is mixed with either the 

 diatomaceous clay, or with clay from another surface deposit not far distant. 

 The green sandy clay, which is the same as that tested from Layton, lies 

 below the level of the yard. 



Another deposit of Pleistocene clay, known as the House clay, is dug 

 about one-fourth mile northeast of the brick works. Here the clay runs from 

 9 to 13 feet in thickness and is underlain by sand. Still another deposit has 

 been located one-half mile northwest of the brick yard. Only the House clay 

 (Lab. No. 1365) and that at the brick yard (Lab. No. 1362) were tested. 

 Their properties are given in the table opposite page 225. 



Although these clays are both surface clays, and occur in the same 

 formation at no great distance from each other, still they are quite dis- 

 similar in many respects. 



No. 1362 is a red-burning clay which burns to a good bright color. Its 

 air shrinkage is not excessive and its fire shrinkage is low. It contains some 

 coarse grit which shows up clearly on the fractured surface of the burned 

 bricklet. At cone 8 portions of the clay become viscous. This is not a fire 

 clay, but it works well for brick and fireproofing. 



No. 1365 is a gritty, light-burning clay which does not burn steel-hard 

 until cone 5, and even at 8 still shows a rather high absorption. Its low air 

 shrinkage and low tensile strength are characteristic of sandy clays. The 

 material can be classed as a low-grade fire clay, such as is used in terra-cotta 

 manufacture, or for boiler-setting brick. It is the most refractory of the 

 series tested from the Coastal Plain area. 



The brick works at Wilmont produce fireproofing, boiler-setting brick, 

 and some front brick. In each case a mixture of the Pleistocene clays, or of 

 these with diatomaceous earth, is used. 



The Layton Area. 



Along the shore of the Eappahannock Eiver, about 1 mile south of 

 Layton, there is a long outcrop of gritty greenish clay, of Miocene age, which 

 is evidently part of a rather extensive deposit. The material is well shown 

 in the river bluff, and its smooth vertical surface stands out in marked 

 contrast to the overlying sand. The bed as here exposed is not less than 9 

 feet thick, and is overlain by 6 to 8 feet of sand, which may be adapted to 

 molding purposes. The clay (Lab. No. 1354) in table opposite page 225, 

 evidently underlies the diatomaceous earth which crops out farther down the 



