OKLAHOMA ACADEMY OF SCIENCE 81 



made t>y the large oil companies on the advice of geologists and 

 engineers who study well records. If the records are good enough 

 to decide such expensive matters, they ought also to be worth con- 

 sidering for the stratigraphic data they may furnish. As a matter 

 uf fact, even in comparison with well made columnar sections, well 

 records have some advantages. The depths and thicknesses are 

 often more accurately given than is possible from surface studies. 

 There are no gaps due to lack of exposures. .A.nd the records are 

 in many districts numerous and easily obtained. 



The value of a well record depends, of course, upon the inter- 

 pretative ability of the man who is to use it. The record, if honestly 

 made, gives the driller's impression of the cliaracter of the rock 

 with which he was dealing. This fact ought to give the geologist a 

 valuable hint, at least, as to the character of the rock. It is impor- 

 tant for the geologist to take as sympathetic an attitude as possible 

 toward the driller and his work. If he does so, he will consider the 

 driller, not as an ignoramus, but as a .skilled workman whose whole 

 life is spent in a struggle with various kinds of rocks. The driller 

 knows no petrography, hut he knows a great deal about how differ- 

 ent rocks affect his drill, and that depends on their properties. He 

 considers rocks merely as obstacles to l)e overcome, but in overcom- 

 ing them he must learn many things aliout them very well. On the 

 basis of these facts of his experience he makes his classification 

 of rocks. 



If a rock drills slowly and abrades the bit, no examination of 

 it is necessary to tell the driller that it is a "sand." It may in some 

 cases actually be a chert, of course, or some other hard rock, but it 

 is usually a sandstone. If it drills slowly but does not "cut the 

 bit," it is a "lime," which examination usually shows to be a lime- 

 stone. Rocks that drill easily are the "shales" and "slates." Con- 

 trary to established petrographic usage, however, the driller's "slate" 

 is commonly the softer of the two varieties. If the rock breaks up 

 into chips which are recognizable as such in the cuttings, it is a 

 "shale ;" otherwise it is a "slate." 



Some other terms used as rock names in the logs from Kansas 

 and Oklahoma are "cave," "shell," "break," "chat," "granite," and 

 "soapstone." Most of these names are of rather obvious meaning. 

 One or two are less obvious. "Shell," for example, is a thin hard 

 stratum that temporarily holds up drilling operations, arid then allows 

 the bit to break through ; thin sandstones or limestones, or bands 

 of ironstone, serve equally well. "Break," on the other hand, is a 

 thin shale stratum separating two harder layers. 



With all that can be done to get at the real meaning of the dril- 



