30 



area is received and conveyed away by an insignificant streamlet^ 

 or when the surface strata are composed of porons beds, by mere 

 occasional storm made currents running in a depression in the 

 surface, but in either case carrying off much spoil of solid matter 

 from the land. 



To denudation by subaerial agents, carried on during the 

 uncounted ages which elapsed whilst the Tertiary Strata were 

 accumulating, I would refer as the principal cause of the 

 formation of these valleys, but believe that when, during the 

 Glacial Period, a change occurred in the relative levels of sea 

 and land, the marine currents running up these narrow valleys, 

 would act with great force, especially by their stirface waves, 

 wearing down the sides, and thereby widening the valleys. 

 During these changes of level the surface of the waters must 

 have acted on a constantly new horizon, for a while rising higher 

 and higher, and then gradually sinMng, thus bringing the force 

 of the surface waves to act on every part of these hill-sides. 

 It is easy to conceive how they would operate to produce cliffs 

 when acting on rocky strata, and uneven slopes when wasting 

 clay beds, also how by wearing away the loosely consolidated 

 sands, and thus undermining the Inferior Oolite, they would 

 produce those extensive landslips which form so marked a feature 

 of this district. It is remarkable how conspicuous are the sands 

 ia these vaUeys, as delineated on the Greological Map, and how 

 seldom they are to be seen in the field, being almost everywhere 

 overlaid by materials derived from higher strata, and are only 

 again brought to view by artificial cuttings, by water- worn lanes, 

 and, occasionally, by running streams. 



If it is conceded that this district was totally submerged 

 during the Grlacial Period, it wiU be interesting to inquire what 

 would be the effect of marine currents flowing over such sub- 

 merged hills and valleys. It is weU known that the bed of the 

 North Sea, of the present day, contains a great number of 

 valley-like depressions. Dr. Ltcett has Mndly furnished me 

 with information on this subject, and on the present action of 

 the currents as they effect the bed of the sea off Scarborough. 

 Of the sub-marine depressions. Dr. Lycett writes : — 



