THE PHYSICAL PROPERTIES OF CLAY. 109 



were determined separately, 5 and 4, and 3 and 2 being grouped 

 together. None of the samples tested contained any gravel. 



If a raw clay is examined under the microscope, it is usually 

 seen to be composed of a number of different sized grains. These 

 may show a wide range of sizes as given in Fig". 30, which repre- 

 sents a gritty clay from the Cape May formation. In other 



Fig. 30. 



Drawing showing particles of a Cape May clay enlarged 362 diameters. 



clays, such as those of the Alloway formation, there is often 

 less variation in the size of the grains (Fig. 31), the grains in the 

 latter being bunched together more than in the former. Figs. 

 32, 33, and 34 represent several sizes of grains from a sample 

 of Clay Marl I which have been separated by the mechanical 

 analysis. Fig. 32 shows the grains of sand enlarged 115 dia- 



