THE CRUST OF THE EARTH 



187 



It takes away soluble minerals in solution, and carries insol- 

 uble fragments with its current to the sea. There the frag- 

 ments are assorted by the ocean currents and finally are made 

 into sedimentary rock. (LABORATORY MANUAL, Exercise 

 XIX.) 



FIG. 96. CATHEDRAL SPIRES IN THE GARDEN OF THE GODS, 

 MANITOU, COLORADO 



These rocks are of soft red sandstone. The highest is more than 200 ft. 

 high. 1. In what position are the layers shown here? 2. What was their 

 position originally? 3. What connection is there between their present 

 position and the rate of erosion? 



209. The Age of the Earth. Just how long a time has 

 been required to bring the earth to its present condition can- 

 not be known exactly. One method of estimating the length 

 of time is by calculation of the average rate of deposit in 

 river deltas whose extent, a few hundred years ago, is 

 known. The time required for the folding into mountains 

 and the wearing down which have followed in some particular 



