Subsurface Laboratory Methods 281 



acteristics and sulphate are negligible; chloride ranges from 3,000 to 

 7,000 parts per million depending upon the concentration; bicarbonate, 

 though, is more erratic and varies from a low of 1,300 to a high of 6,000 

 parts per million. 



In contrast to Mush Creek, the Newcastle-sandstone waters at Skull 

 Creek are alkaline and vary from 6,000 to 8,000 parts per million total 

 solids. Secondary characteristics and sulphate are negligible, chloride 

 ranges from 800 to 2,000 parts per million, and bicarbonate from 4,000 

 to 6,000 parts per million. This, the author believes, is evidence that the 

 Skull Creek waters have been modified by meteoric water to a greater 

 extent than the Mush Creek waters. 



Lower Cretaceous 



Lower Cretaceous beds include the Cloverly formation of Wyoming 

 and Colorado, the Greybull sandstone and Pryor conglomerate of south- 

 central Montana and the Big Horn Basin of Wyoming, and the Kootenai 

 formation of north and north-central Montana. These beds produce oil 

 at various localities in Wyoming and Colorado, and the Kootenai is one 

 of the principal oil- and gas-producing formations of Montana. 



In general, Dakota(?) waters of Colorado are relatively dilute, soft, 

 and alkaline, with concentrations ranging from 700 to 3,000 parts per 

 million total solids and with an average of about 1,500 parts per million 

 total solids. Wyoming Dakota(?) waters are quite variable; where as- 

 sociated with oil or gas, concentrations as high as 20,000 parts per million 

 total solids are encountered, but where not associated with hydrocarbon 

 accumulation dilute waters are the rule. Kootenai waters range from about 

 1,000 parts per million at Cat Creek to as high as 15,000 parts per million 

 total solids at Cut Bank and on the average seem to be more concentrated 

 than equivalent waters in Colorado and Wyoming. 



Dakota(?) and Kootenai waters as a rule are more alkaline than 

 Upper Cretaceous waters previously discussed. Alkalinity is the impor- 

 tant distinguishing feature between Colorado and Kootenai waters in 

 Montana, the bicarbonate content of Kootenai waters being appreciably 

 higher. Exceptions to this rule in Wyoming, however, are numerous, the 

 North Baxter Basin gas field being an example of high salinity and low 

 alkalinity; the Beaver Creek gas field also violates the general rule, as 

 do Salt Creek and Church Buttes. 



The Dakota(?) and Lakota sands more often than any other forma- 

 tion yield potable water in Wyoming. This is particularly noticeable 

 along the eastern edge of the Powder River Basin and in the Poison Spider 

 area of central Wyoming, where the sands are not deeply buried and crop 

 out on nearby uplifts. 



Table 11 lists a number of the more important Lower Cretaceous 

 waters of the Rocky Mountain region. 



