RELATIVE RATES OF DEPOSITION 



907 



ried out in an experimental tank. Tliese were designed to show the con- 

 trast in the character of beds laid down where salinity was the only factor 

 which differed in the two experiments. Fresh water was used in the 

 first and salt water in the other experiment. In both cases clay, pow- 

 dered chalk, and sand were introduced in the same order and amounts, 

 and the same time intervals for settling were allowed. The materials 

 were introduced in the form of aqueous mixtures by means of a small 

 stream of water pouring slowly into the settling tank through a tube. 

 The results of the two experiments are shown in the two photographs 



i^'iuiJEE 1. — Photograph of a Section formed in salt Water 



The section, as seen through the side of the glass tank, consists of three beds of chiy, 

 two beds of powdered chalk, and a bed of sand at the top of the series 



reproduced as figures 1 and 2. Figure 1, which represents the tank with 

 saline water, shows a series of sharply defined beds, consisting of three 

 bands of clay separated by two beds of chalk and a bed of sand termi- 

 nating the section. In figure 2, although the same materials were used 

 in the same quantity and order, the resulting section is materially differ- 

 ent. Even the order of superposition is different. The sand, instead of 

 lying at the top of the section, lies below the top, under a half-inch bed of 

 clay, although the clay was introduced several hours before the sand. 

 The fresh-water section thus fails to iiulicate the true order iu which the 



