IN THE GLACIAL DKI'USITS AT H K.N DON. 577 



luive been ])ro(luced by ice-action ])ri()r to tlie (lepositi(ni of the 

 (iravels in them. At the eastern end of the \v.t the Upper Boulder- 

 clay, like that mentioned as occurring in the Green Lane and 70 

 feet lower, contains many decomposed patclies and concretions of 

 carbonate of lime resembling the "' race '' found in some brick-earths. 

 Here the " race " occurs most abundantly near the base of the 

 clay. Mr. AVhitaker, in describing. the Glacial deposits at Church 

 End, Finchley*, refers also to tlie fact that the brown clay there 

 found underlying the Chalky Boidder-clay contains much " race." 

 The resemblance between this brown clay, when, as is often the case, 

 it contains scarcely any pebbles, and the London Clay is particularly 

 striking, and leads one to the conclusion that much of the brown 

 clay must have been derived by denudation from exposed surfaces 

 of London Clay during the Glacial period t- 



There are several patches of sandy gravel enclosed in the Upper 

 Clay in this pit which, it is clear, must have been torn off as frozen 

 masses from underlying beds and re-deposited as boulders in the 

 clay. The sandy gravel in these patches of tens exhibits a rough 

 oblicjue stratification, and the materials seem to be identical with 

 those in the underlying gravels here and elsewhere in the neigh- 

 bourhood. Over the surface of the clay, and filling some depres- 

 sions in it, a rough gravel is frequently found, the result probably 

 of the subsequent denudation of the Boulder-clay by sub-aerial 

 action and flood-waters at the close of the (glacial period. This 

 gravel has been spread out very generally as a thin coating over 

 the neighbourhood, and extends beyond the line on the Map, which 

 is intended to indicate the boundary of the more typical Glacial 

 deposits. 



As this gravel contains many white-coated fresh-looking flints and 

 subangular fragments and some northern erratics in association with 

 the well-rolled pebbles from the Tertiary beds, it is evident that it 

 must have been derived immediately from a Boulder-clay which 

 had been spread out very universally over the area, especially as it 

 is now found not only on most of the hills and slopes east and 

 west of the Hendon plateau, but also between it and the Thames 

 Valley. 



In the section (fig. 1, see next page) which was recently exposed at 

 the S.E. corner of the pit A, the rough gravel at the base contained 

 many angular masses of sarsen-stones and large flint blocks, some of 

 the latter being but little worn and having white-coated surfaces. 

 The majority of the flints, however, here as elsewhere, are w^ell-rolled 

 pebbles, and must have been derived by denudation from Eocene beds 

 in the neighbourhood. There were also numerous fragments of chert 

 and ferruginous sandstone, evidently derived from the Lower Green- 

 sand, and also some pebbles of quartz, quartzite, ironstone, «S:c. In 

 this pit the lower rough gravels vary in thickness from 2 to 4 feet, 

 according to the irregularity of the floor. Between the sandy gravels 



* ' Geology of London ' (1889), vol. i. p. 311. 



t !Mr. II. B. Woodward refers also to this resemblance, and says that this 

 clay is " often Aery like London Clay," o/j. cif. vol. i. j). :V){). 



