n6 



THE GLACIAL GEOLOGY OF NORTHUMBERLAND 



Map No. 3. 



The shaded areas marked P and G indicate the outcrops of Cheviot porphyrites 

 and granites ; the irregular black patches, the outcrop of the Whin Sill. With the 

 exception of the dykes and a few minor exposures of other igneous rocks, the rest of 

 the country is occupied by sedimentary rocks, mostly of Carboniferous age. 



The arrows show the direction of ice movement at the various stages (numbered 



I, 2, and 3). The broken lines ( ) refer to the earliest stage of glaciation (1), 



the lines and dots ( .. ) to the stage of maximum glaciation (2), and the 



unbroken lines to the period of melting and retreat (3). 



The line AA marks the western limit of drifted Cheviot rocks; BB, the northern 

 limit of Scotch (Galloway) granites ; CC, the northern limit of Lake District rocks, 

 and the two lines DD, the limits of sedimentary drift in the Cheviot area. 



The lines DD also represent the position of confluence of native Cheviot ice with 

 foreign ice at the period of melting and retreat, and EE the line of confluence of 

 the western and northern ice-sheets, south of the Coquet, at the same late stage. 

 It is in the immediate neighbourhood of these three lines that the swires are most 

 extensively developed. 



The upper Cheviot drift occurs abundantly in the tract between the dotted lines 

 (the continuations of DD). 



