Vol. V] DUMBLE— TERTIARY DEPOSITS IN NORTHEASTERN MEXICO ^55 



INTRODUCTION 



In connection with the examination of the artesian water 

 conditions of Northeastern Mexico, and the search for oil de- 

 posits in the same region, a considerable amount of geological 

 investigation has been necessary. The field work with which 

 the writer has been directly connected was carried on prin- 

 cipally by Prof. W. F. Cummins, assisted by Mr. J. M. Sands. 

 Mr. W. Kennedy also spent some time on more detailed work 

 along the Rio Grande and in making special sections. In 

 order that the information thus obtained may be of service to 

 other workers in this same field, the following generalized 

 statement has been prepared from their various reports and 

 collections and from personal knowledge of the deposits. 



It must be remembered that the work has largely been of 

 the nature of a reconnaissance and that it has been done with 

 a total lack of topog'raphic maps and in part even without 

 those giving accurate geographic detail, since these were not 

 available until after the field work was completed. It is also 

 to be regretted that while large collections of fossils were 

 made during the progress of the work, only a small part of 

 these were accessible for use in preparation of the present 

 paper. 



