550 C. N. GOULD CRYSTALLIXE EOCKS OF THE PLAINS 



wide. Gilbert, in Journal of Geology, volume IV, page S21, says : 'Fragments 

 of various rocks are included in the laccoliths and dikes, and are of interest 

 as revealing the nature of the lower lying terranes through which the ascend- 

 ing liquid passed. Besides sandstones and shales similar to those constituting 

 the wall rocks, the most abundant as well as the most notable rock is a 

 porphyritic granite with conspicuous crystals of gray feldspar.' This suggests 

 his belief that the granite is an inclusion in or mass floated up by the basic 

 igneous rocks forming the laccolith. There are at least three granite lacco- 

 liths, but I am not entirely certain that the two smaller granite masses are in 

 place. While I have made no petrological examination of the granite, its 

 general appearance suggests quartz monzonite rather than a true granite." 



Subsurface crystalline Eocks 

 general statement 



It is, however, chiefly with subsurface igneous rocks that this paper is 

 concerned. We may safely say that within the past five years our knowl- 

 edge of the subsurface geology of the Great Plains, especially in certain 

 parts of Oklahoma, Kansas, and Texas, has increased several hundred 

 per cent. This condition has been largely brought about, either directly 

 or indirectly, by the work of the geological departments of the various 

 oil companies. In these States the geologist is now considered as an 

 integral part of any oil organization, and his advice is not only sought, 

 but acted upon, by men making large investments of time and money. 



A number of highly trained and very efficient men, young men for the 

 most part, in these States are now devoting the greater part of their 

 time to subsurface work. Logs of wells are studied and compared, and 

 in this manner many subsurface structures of which there are no surface 

 indications sometimes have been plotted. Considerable literature is al- 

 ready accumulating on the subject, but the most comprehensive paper 

 on subsurface crystallines was published by Sidney Powers.^^ 



The net result of the work of the various geoloo-ists who are now work- 

 ing on subsurface problems has been to throw a vast amount of new light 

 on the underground stratigraphy and structure of the region. Unfortu- 

 nately, much of the material collected is not yet available to the public, 

 largely for the reason that relatively few of the oil companies have yet 

 reached the stage where they can afford to be philanthropists ; also, many 

 of the managers of these companies, being anything but scientific men, 

 have not yet been brought to appreciate the true worth of broadly dis- 

 seminated scientific investigation. There is still much needless and ex- 

 pensive duplication of work and much attempt to conceal data which 

 would be of the greatest value in the solving of vital problems. Never- 

 theless, each year more and more new facts are coming to light and the 



