refusion of sediments as factor in magma genesis 447 



Summary 



When a core sample of the beds penetrated is taken during the drilling 

 of an oil well, it is found, nnder some conditions, that part of the core 

 consists of a slaglike mass bearing some resemblance to a natural lava. 

 This slag has been pronounced by some geologists to be the result of 

 fusion of rock in the drill-hole as a result of the heat of friction, though 

 some operators have been unwilling to accept this conclusion. The ex- 

 amination of two drill cores sent us by Prof. Bailey Willis, in one of 

 which the beds immediately above the slag were well jDreserved, has con- 

 firmed the opinion that the slag is the result of fusion of the sedimentary 

 Tock in place. Chemical analyses of sediment and slag show that they 

 are practically identical in composition, except that the fused part or 

 slag has lost nearly all its .water, all its CO2, and about one-half its sul- 

 phur, and has received a considerable contribution of iron from the drill 

 pi|)e. 



Thermal tests in the laboratory show that a temperature nearly, if not 

 quite, as high as 1,150 degrees centigrade is necessary to produce the 

 results actually obtained in drilling. A metallographic study of the steel 

 shows that the temperature attained was 1,050 degrees centigrade or 

 higher. 



The chemical composition and the microscopic characters of the ma- 

 terial fused show that it was of the nature of an arkose, a variety of 

 sedimentary rock which appears to be particularly susceptible to such 

 fusion. Since the rock was an arkose, the slag shows only a moderate 

 departure in composition from an igneous rock, but the difference is 

 none the less real and is in the same direction as that exhibited by typical 

 shales. On account of the arkosic nature of the sediment the general 

 chemical similarity of the slag and igneous material can not be regarded 

 as affording any support to the theory that igneous rocks are formed by 

 the fusion of shale, nor do the thermal results favor the view that remelt- 

 ing of shale could occur at moderate depths in the earth's crust (say 

 6 to 10 miles) unless the normal temperatures prevailing at such depths 

 are notably augmented by intrusion of igneous matter from greater 

 depths. 



Discussion 



Dr. Sidney Powers : This paper is interesting from the viewpoint 

 of petroleum geology. These cores are taken with the rotary system of 

 drilling, and an ordinary piece of pipe is attached to a sawtooth edge 

 which is all rotated Avith whatever mud happens to be in the hole. The 



