THE GRAVEL PIT. 19 



Now we wish to know more about the internal constitution 

 of this deposit. This will be easy, for the Drift is all about 

 us, and numberless deep excavations have been made for sun- 

 dry purposes. Let us visit a gravel pit, or some deep railroad 

 cut through a pile of these incoherent materials. 



Do you find these loose sands and gravels arranged in 

 regular courses ? Yes, you say ; and then you hesitate ; and 

 well you may; for the semblance of courses is exceedingly 

 interrupted. Here is indeed, a layer or bed, or stratum of 

 sand, but it thins out in one direction, and in the other, 

 loses its upper and lower boundaries, and merges in a general 

 mass of sand. Here is a bed of gravel, but it lies at a dif- 

 ferent inclination from the last, and in one direction it changes 

 to sand, while in the other, it becomes split up into a num- 

 ber of subordinate layers which bend down and lose themselves. 

 This bed also is composed of many oblique laminae, coarser 

 and finer in alternation, which are cut off completely by the 

 upper and lower surfaces of the bed or stratum. What is 

 singular, the very next bed below this, which is also obliquely 

 laminated, has its lamina tilted in the opposite direction. 

 And then next to this is a long straight course of cobble- 

 stones and pebbles. Is not this a correct description of what 

 you have all seen somewhere ? 



In some places are large' beds of fine sand, which are 

 taken out and used for mortar-making. In others we find 

 extensive deposits of gravel and pebbles, which are used for 

 paths and streets. Mixed in the sands are some cobble-stones 

 and large bowlders. Here and there, too, are some beds con- 

 taining much clay ; and these are impervious to water. Now, \ 

 all this is not a regular nor a perfect bedding or stratification. 

 We may say the Drift here is semi-stratified. You can all 

 recall some locality where this arrangement of materials 

 occurs. 



This cut or exposure, however, extends only fifteen or 

 twenty feet down. How is the arrangement below? There 

 are places where the bed-rock is not reached in less than a 

 hundred or two hundred feet. There are wells fifty to eighty 



