tion published as GW-1, collection of well logs and reports of borings, a geologic study of the 

 western end of the island — Bulletin GW-7 — and a general engineering report — Bulletin GW-2 

 — including redetermination of ground water levels, discussion of the whole problem, pointing 

 out of the additional information needed, suggestions and tests as to methods of showing the 

 various structures and an outline of the hydrologic questions. 



In continuation of this work, all available well logs were collected, edited by the U. S. 

 Geological Survey, and have been published in the GW series of pamphlets. There are now two 

 volumes of well logs for each county (GW — 3 to 6 and 8 to 11) . 



It became apparent that the original concept of a single body of ground water underlying 

 the whole island must be modified and that for purposes of study, each aquifer should be con- 

 sidered as a unit, although there appear to be numerous interconnections between them. To do 

 this required an intensive geologic study of the well logs and the development of a method of 

 delineating the formations and aquifers so as to show them in three dimensions and in better 

 fashion than was done by Professor Crosby's sections. These last were drawn by projecting 

 well logs, frequently somewhat remote onto selected sections, a method which fails to give 

 satisfactory results. 



With such data at hand, more elaborate studies of hydrologic conditions will be possible. 



To do this work the present appropriation was asked for and the work has proceeded as 

 well as the critical shortage of manpower would permit. 



A new cooperative agreement with an allocation of funds to the Geological Survey pro- 

 duced the geological correlations of well logs contained in this report. The well census was ex- 

 tended over the whole island. All known wells have been assigned numbers, have been plotted 

 on sectional maps and data with regard to them have been filed and classified. The contour maps 

 contained in this report were prepared and profiles drawn from them. These it is proposed to 

 amend from time to time as more data become available. 



These maps on a larger scale and a full set of profiles have also been made available in 

 Bulletin GW-19, "Ground Water Atlas of Long Island," which can be obtained as a whole or 

 as separate sheets from the Commission. 



The Commission has not yet been able to secure the services of suitable men to carry on 

 the proposed hydrologic studies and that work has perforce been left to the future. The need 

 for it is imperative. 



The data given here are in many cases disappointingly vague, must contain many errors 

 and certainly lack greatly in precision. But, they are the best that now can be obtained and the 

 maps have been drawn, with them as a base, with as much accuracy as is possible. As the data 

 are increased by later additions, the maps and profiles will be amended and kept up to date. 



In spite of the unsatisfactory condition of the basic data, it is thought that these maps even 

 now will serve as a basis for much needed and contemplated studies of water levels, salt water 

 intrusion, recharge and interconnections of aquifers which heretofore have been impossible. 



At the end of this report will be found a schedule of references and a statement of the well 

 information on file in the Long Island office of the Commission, where they are available for 

 public inspection and use. The Commission invites such use and its employees will be glad to 

 aid the public in using it. 



