4 NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA, 



For convenience' sake we have thought it desirable to 

 classify the records according to locality. The map contemplated 

 by the Union not yet being published, we have been led to make 

 for our purpose a division of the county into 24 Districts, based 

 upon its physical configuration; note being also taken as far as 

 possible of the geological features. In tracing the boundaries of 

 the various districts, it has been found desirable to adopt arbitrary 

 and easily defined lines where nearly coincident with the true 

 line. The central district is almost entirely defined in this 

 manner, while the other districts can be very conveniently based 

 on the river-basin system. 



The manufacturing districts of the South-West being much 

 more minutely investigated than other parts of the county, 

 subdivision has been carried to a greater extent in this part. 



In defining the following districts we have not space to do 

 more than give a sufficient indication to enable our readers to 

 trace them for themselves v\-ith the aid of the Union Map (when 

 published), of those of "West Yorkshire," and other documents. 



Of the 24 Districts, 22 drain eastward into the German Ocean, 

 while the following 2 are in the 



WESTERN DRAINAGE SYSTEM. 



1. Mersey. — The Saddleworth district is separated from 

 the remainder of the county by the vrater-shed line on the crest of 

 Standedge Moors. 



2. Lune and Ribble. — Separated from the rest of the 

 county by the water-shed line running nearly due N. and S. 



EASTERN DRAINAGE SYSTEM 



3. Vale of York. — Bounded by the Railway from Arth- 

 ington past Knaresbro', Boroughbridge and Malton as far as 

 Burdale Station — thence by road S.W. past Raisthorpe, Gills, 

 Pluckham, Huggate, Warter, Burnby, Hayton and Beilby, to 

 Harlthorpe Station — thence by the Railway through Selby to 

 Crossgates Station — thence by water-shed line to Arthington. 



4. Humber. — Bounded on the North by the Central 



Traiis.y.N.U., 1877. Series C 



