NO. 4 FORAMINIFERA CUSHMAN 3 



INTRODUCTION 



The foraminifera are for the most part microscopic animals living 

 in salt water. There are a few which live in fresh water or under 

 brackish conditions, but they do not develop the typical test and are 

 not found as fossils. The foraminifera belong to the general group 

 of the Protozoa. They are single-celled animals which develop about 

 them a test either of foreign material, which they gather and cement, 

 or usually a calcareous test which is secreted by the animal itself. 

 In the present oceans they occur in enormous numbers, making up 

 a large proportion of the material forming the floors of the oceans 

 at moderate depths. As fossils they have formed limestones thou- 

 sands of feet thick in various parts of the world. The great pyramids 

 of Egypt are composed of limestones of foraminiferal origin. In the 

 tropical Pacific they occur in such great numbers that they often 

 impede navigation in shoal waters among coral islands. 



Until recent years their study has been largely a matter of pure 

 science, and their interest confined, except in a general way to zoolo- 

 gists, to a small group of workers. In the last few years, however, 

 they have assumed an importance for economic work. They occur 

 in great numbers as fossils in most of the Tertiary and Cretaceous 

 strata. Especially in connection with the petroleum industry they 

 have great present and future possibilities. In the drilling of wells 

 most fossils are so broken up that they become unrecognizable in 

 the samples. The foraminifera, however, are usually of such minute 

 size and are in such quantities that enough of them escape the destruc- 

 tive force of driving so that they form a recognizable part in the 

 well samples themselves. By close study of the section through which 

 a well is drilled it becomes possible to recognize various zones which 

 may be again found in adjacent wells. By such study subsurface maps 

 may be made, which show the geologic features of the underground 

 structures. By this means it is possible to control the placing of 

 additional wells in a field with greater or lesser certainty of increase 

 in production. Where the age of the strata is not definitely known 

 a well may be abandoned before it actually reaches a producing horizon 

 or may pass through such a horizon for a considerable distance with- 

 out its being recognized. In either case a considerable economic loss 

 results. The knowledge that might have been obtained from the 

 borings is also lost. In many oil fields it is necessary to shut ofif 

 underground water, and these water horizons may be recognized by a 

 study of the foraminifera. This again is a great economic use of these 

 small fossils. 



