Past experience has taught the geologist that oil-bearing formations manifest themselves by certain surface indications, such as gas springs, and surface seepages of oil or asphalt. In an untested field the expert studies the character of the successive formations along such outcroppings. In any mountainous region earthcrust upheavals during past ages have exposed a series of formations, similar to those which lie deep below the surface of the plains. Thus it is possible to predict with a fair degree of accuracy just what the formations will be for a considerable depth from geological indications. Geologists have also learned to recognize certain types of structures favourable to the accumulation of oil pools, known as anticlines, synclines, salt domes, monoclines and so forth. Thus it is sometimes possible to make in advance of drilling a surprisingly accurate forecast of what these operations will reveal. Because for the most part oil fields exist in rather sparsely populated districts, remote from centres of commercial and industrial activity, the general reader has probably very little knowledge of the unceasing efforts that are being made in many parts of this country to maintain the supply of crude oil at an adequate level through new discoveries. The spirit of enterprise and initiative is even more alive to-day than it was in the time of Drake and the pioneers who followed him in the Pennsylvania field. The hopeful speculative spirit is as ever necessary; the capital fulfils an ever-growing function in this source of prosperity and employment for the community at large. In the oil industry any well drilled outside the narrow limits of a producing “pool” is regarded as a “wild cat” test. The element of a gamble is inevitably present, but has been materially reduced by science. An old established company in an important field is constantly adding to its land holdings in advance of the trend of development, and out of the profits from its developed productions sets aside a certain amount to expend for speculative ventures, to protect its investment in pipe lines, refineries, etc. The company also continues to drill in the vicinity of a producing pool until it is entirely surrounded by dry holes, and its limits demonstrated. Consequently, in an established oil field development work and prospecting are one and the same thing.