Luther — Geology of the Salt District. 



209 



have settled down into it. They are full of seams and grains of salt, and 

 when subjected to the dissolving action of water, either separate into angular 

 fragments in which there are many irregular cavities, or become reduced to the 

 consistency of dark grey sand. 



The roof of the salt bed is composed of large and small blocks, usually of 

 gypseous shale, of the character described, the spaces between the blocks 

 sometimes several inches in width, being filled with salt. 



These veins were found to extend upward through shales and limestones, 

 coalescing or branching out, twenty-one feet into the overlying strata at the 

 Livonia shaft and more than 200 feet at the Lehigh shaft. 



The salt in these veins is usually columnar or in crystals about the size of 

 those in solar salt, and, in the shales, is frequently colored red, owing to the pres- 

 ence of iron. At the Greigsville and Lehigh shafts some of this vein salt is 

 blood red. Thin veins and seams of gypsum are also abundant in the rocks 

 and sometimes have the same red color. 



Veins sometimes occur in which the matter adjacent to the walls is 

 gypsum, and a layer of salt forms the middle portion. 



The existence of these veins is the cause of much trouble in the salt wells. 



The lower end of the tubing through which the brine comes to the surface, 

 is placed in the lower part of the bed in order to reach the fully saturated 

 brine which increases in weight as it takes up salt, and consequently sinks to 

 the bottom of the cavity that is rapidly formed by the removal of the salt. 

 The dissolution of the salt releases the embedded fragments of rock and 

 gypsum and, except such small particles as the upward current in the tubing 

 may cany to the surface, they are deposited on the floor of the reservoir. 

 After a time, as this process is continued, the heavier strata overlying the 

 salt lose their support and disastrous cavings take place, heaping the debris 

 about the bottom of the tubing and preventing the inflow of the brine, 

 frequently making it necessary to drill out the well, and instances have 

 occurred where the tubing has been broken oft' by the falling rocks. As these 

 cavings are known to occur in all parts of the salt district, the inference is 

 warranted that the condition of the salt bed and also of the superjacent rocks 

 is the same over the whole district. 



The total thickness of the rock salt beds, including the interstratifled 

 layers of shale and limestone, in the southern part of the Oatka valley, is from 

 100 to 135 feet. At Silver Springs it is 145 feet, and at Castile 190 feet. 



They gradually thin out toward the north, and do not reach beyond the 

 latitude of Batavia, Le Boy and Caledonia. 



