THERMAL CONDUCTIVITIES OF ROCKS 285 



Period of cooling.— It would seem reasonable to believe that the tempera- 

 ture of the rocks that had been exposed to cooling would be less than that 

 of rocks that had never been exposed. No decisive opinion is yet justifiable. 



Problem of unconformities. — This problem is mentioned by the author as 

 being a complex one and requiring more study. 



Relation of earth temperature to structure. — A regional picture con- 

 structed to show about half the State indicates a belt of comparatively high 

 temperature along the Balcones-Mexia-Luling fault in which the tempera- 

 ture increases with depth at the rate of i° F. for about 43 ft. In the central 

 region that temperature increases i° F. for each 50 to 60 ft. Farther west 

 and north-west the average rate of increase is less than i° F. for about 100 ft. 

 The few data available for the great basin of west Texas show that the basin 

 cannot be outlined merely by studying the temperature conditions in wells 

 drilled in and near it. For example, in two wells about 25 miles apart, 

 the temperature in one increased at the rate of i° F. for every 84 ft., and in 

 the other i° F. for every 137 ft. 



Big Lake field. — The structure of Big Lake field is clearly reflected by 

 the temperature measurements. 



Salt domes studied. — Four domes (three of them in the Gulf Coast 

 region) were observed. The work has shown that, in so far as this type of 

 structure is concerned, the presence or absence of oil has no determinable 

 effect. General outlines of salt domes can, of course, be located by measure- 

 ments in very shallow drill holes. 



Concentration of heat. — In neither area has the work been done in 

 sufficient detail to justify conclusions as to the probable conditions re- 

 sponsible for temperature variations. 



Regional metamorphism. — The idea that the amount of pressure to which 

 a region has been subjected should be reflected in the temperature is not 

 supported by the work in Texas. 



California. 



Geologic conditions. — The rocks involved in the California measurements 

 represent a very short period of geologic time. In comparing the results 

 of the California work with those obtained in the other States, the author 

 expresses his preliminary impression that time is not a factor having an 

 important influence on temperature variations in the earth. 



Plan of work. — The Santa Fe Springs field was chosen for exploration, 

 and more than thirty wells have been measured in that field. The data 

 •secured in California must be considered dependable, as some of the 

 measurements have been repeated ; they were also retested by C. E. van 

 Orstrand, who used different instruments from those employed by A. J. 

 Carlson. 



Results. — A report giving details of the work has been prepared by A. J. 

 Carlson and is in process of publication by the American Petroleum 

 Institute. 



Relation of temperature to petroleum. — The work in California has so 

 far contributed nothing to help to decide whether or not petroleum itself 

 is directly or indirectly responsible for abnormal earth temperatures. 



Relation of temperature to circulating waters. — Although some of the 

 fields of the San Joaquin Valley have been studied in detail so that it is 

 possible to outline with reasonable accuracy areas in which certain sands 

 contain waters that are moving downward from the outcrop and other 

 areas where the waters are either standing still or are moving up towards 

 the outcrop, no temperature work has been done in these areas as yet. 



