Fifteen years ago petroleum geology was in its infancy. At that time some field mapping for oil had been accomplished in Kansas, Wyoming, and Oklahoma, but very little had been done in Texas. The real impetus to this branch of geology in Texas followed the discovery of oil at Ranger, in Eastland County. This was in 1917. In the same year, at Tulsa, after having held several informal meetings in 1915 and 1916, the South‐western Association of Petroleum Geologists was permanently organized, one year later to become the American Association of Petroleum Geologists (18).2 At the end of 1918 and in 1919 the ranks of those applying their knowledge to the search for oil were greatly increased by geologists returning from the World War. These dates are mentioned as a background for the subject of the present paper. It is the writer’s aim to point out briefly how far . . .