168 JV. H. Darton — Geothermal Data, etc. 



Pierre and extending far to the southwest, south and southeast, 

 and culminating at Fort Randall ; the long area of moderately 

 thermal district extending eastward along the latitude of 

 Pierre, from Miller, Wolsey, Huron and Iroquois ; the area of 

 relatively cool underground conditions extending westward as 

 a tongue through Mitchell, Plankinton, White Lake and Kim- 

 ball, and southward towards Tyndall, and the similar oblong 

 area extending through Britton towards Aberdeen. In con- 

 sidering the data it was at once observed that these features of 

 areal distribution were closely similar to the configuration of 

 the " bed rock" surface. Accordingly I have given, in fig. 2, 

 a contour map of this surface for comparison. The long area 

 of the cooler underground conditions from Mitchell to Kim- 

 ball will be seen to be almost coincident with the underground 

 ridge shown in the figure. This ridge is mainly of Sioux 

 quartzite. The area of higher temperatures just north is 

 approximately along the bottom of the valley in the " bed 

 rock," which extends from Madison through Huron and south 

 of Wolsey. Beyond these very striking features the resem- 

 blances are not noteworthy, but those above pointed out 

 strongly suggest that the cooler area extending from Kimball 

 to Salem is in some way related to the presence of the ridge of 

 crystalline rock beneath the surface. 



This brings us to the question of the cause of the thermal 

 conditions in the Dakota artesian basin, bat no satisfactory 

 solution has as yet been suggested. So far as we know there 

 are no metamorphic processes nor orogenic movements in 

 progress in this region which would give unusual underground 

 heat. The suggestion of the oxidation of pyrites by under- 

 ground waters is probably untenable on account of the depth. 

 Several ideas have been considered, comprising one that pos- 

 sibly some glacial chilling still remains in the ridge of " bed 

 rock"; another of different ratios of conductivity, and a 

 third, that the process of induration now probably in progress 

 in the sediments is giving rise to heat ; but many difficulties 

 preclude their acceptance in our present state of knowledge. 



This investigation is to be extended as widely as possible, 

 and preliminary to this end I am now making a canvass of all 

 available underground temperature observations in the United 

 States so far as noted. I shall be very glad to receive data 

 from geologists and others. 



