$8 DR. J. A. SMYTHE ON 



He writes on the subject as follows : " The gravel beds differ 

 from the boulder clay as to the source of their rocks ; in the 

 former the rocks are chiefly those which are not found in situ 

 in the immediate neighbourhood ; in the latter the boulders 

 are chiefly of local origin" (p. 352). The gravels referred to 

 in this extract are charged with Cheviot porphyrites, which 

 are so abundant in places as to be the main constituent, and 

 this Upper Cheviot Drift, as it may be called, can be traced 

 down the valleys of the Aln and Eglingham Burn, through 

 Alnwick and Alnmouth and southwards in a sinuous line, 

 from two to six miles from the coast, through Crowden Hill to 

 Whitefield on the Wansbeck. A conspicuous mound of the 

 same porphyrite gravel occurs by the Haydon Letch, two 

 miles north of Ashington. Similar porphyrite-bearing gravels 

 overlying boulder clay containing chiefly local rocks have 

 been described by Garwood [21]. They occur near Budle. 

 Another striking example of the same phenomenon occurs in 

 the valley of the Erring Burn, the kaims of which contain 

 Lake District rocks and Galloway granites in abundance, but 

 are practically free from whin pebbles, though the Whin Sill 

 crops out only a mile or two to the north-west, and the 

 country around is strewn with erratics derived from it. 



Two gravel beds may now be referred to, which are exposed 

 on the coast and contain a variety of rocks, some of which 

 have not been noted as occurring in the boulder clays. One 

 is exposed at Horsebridge Head about half-a-mile north of the 

 mouth of the Wansbeck. It occupies a valley-like depression 

 in Carboniferous shale and sandstone, and is overlain by 

 typical boulder clay. The contents are chiefly local sand- 

 stones; Carboniferous limestone is rare, dolomitic limestone 

 (with Permian fossils) common ; many chalk flints and one 

 pebble of chalk have been found. Of the igneous and 

 metamorphic rocks present, whinstone is the most abundant, 

 porphyrites, many of undoubted Cheviot origin, are common, 

 and, in order, come granites, mica and hornblende schists, 

 syenites, quartz porphyries, andesites and glossy porphyrites 

 (Cheviot), mica porphyrites and diorites. Though the mode 



