2 BULLETIN 502, U. S. DEPARTMENT OF AGRICULTUEE. 



wet ground usually occurring near an underlying shale ridge, point, 

 or knoll which discharges water into the soil immediately surround- 

 ing it. 



The possibility of reclaiming the water-logged and alkaline shale 

 lands has been demonstrated in numerous instances; the purpose of 

 this bulletin is to explain how and why the shale enters into the 

 problem and to present the principles and methods upon which the 

 reclamation of this type of land depends. 



GEOLOGICAL FEATURES. 



In the drainage of shale lands some knowledge of the underground 

 formations is essential, as the seepage water often is under pressure 

 and the problem is similar in some respects to one of developing an 

 artesian supply. The water may move for considerable distances at 

 depths that can not be reached by drains and may appear on the sur- 

 face at some lower point. Ordinary methods of drainage fail because 

 of the pressure and the resulting upward movement of the water. A 

 proper solution of the problem requires a careful study of the source 

 and direction of ground-water movement. Obviously, this necessi- 

 tates a knowledge of the strata carrying the water. 



The area to which this bulletin pertains is situated in the Eocky 

 Mountains and on the high plateau areas immediately adjacent. The 

 land usually is at a high elevation, the slopes steep, and the topog- 

 raphy very rough. The rivers usually are hemmed in by high rock 

 bluffs where they emerge from the mountains into valleys that are 

 more open and gentle in slope. These valleys often are characterized 

 by a sharp ascent to a gravelly mesa on one side and by a long 

 gradual slope on the other side. Some distance back from the stream 

 the ascent is broken by terraces of gravel or sand, or by tracts of 

 clayey " bad lands," and here and there by rocky cliffs and mesas. 



Shale is a finely stratified or laminated rock, formed from the strati- 

 fication of clay, silt, or mud. In some of the so-called paper shales 

 (Plate III, fig. 2) there are as many as 30 or 40 laminae to the inch, 

 each representing a separate stage of stratification. 



Numerous varieties of shale structures are encountered which in- 

 fluence the movement of the underground water; however, this dis- 

 cussion is limited to the following three distinct types that have a 

 wide range: Type No. 1, hard, calcareous shales that have suffered 

 little or no displacement ; type No. 2, shales, the layers of which dip 

 very steeply ; and type No. 3, shales in which the layers are horizontal 

 or nearly so, but which have been subjected to great pressure. 



Shales of the first type need little description. Being hard, poorly 

 laminated, and lacking fissility, they more nearly represent the popu- 

 lar conception of shales which classes them among the less pervious 

 geological strata. They probably are not capable of containing more 



