part 1] LITTLE HEATH SA^DS A^ T D GEAVELS. 45 



small blocks of foreign material, such as Bunter pebbles (liver- 

 coloured quartzite, etc.), vein-quartz (often in large angular or 

 subangular fragments), Carboniferous Limestone, sandstones of 

 various ages, waterworn fossils (especially Gryphcea) from the Lias, 

 Oxford Clay, etc., special types of rock such as Red Chalk and 

 Spilsby Sandstone, many igneous rocks, and in a few localities, 

 fragments of Scandinavian rocks. Now, these foreign components 

 have obviously come from a considerable distance ; they are far- 

 travelled. 



But the gravels on the Tertiary Ridge, selected as the type of 

 High-Level Gravels, contain no far-travelled material. The chief : 

 pebbles foreign to the district consist almost exclusively of small 

 pebbles of white quartz and of lydite ; Lower Greensand chert is- 

 fairly common in part of the area. These small pebbles have been 

 derived from the Lower Greensand. They can be seen pouring 

 out of the end of water-sieves or screens in operation at Leighton 

 Buzzard, where the incoherent Lower Greensand is sieved for 

 commercial purposes on a considerable scale. There are certain 

 points in these pebbles that help to establish their identity. Many 

 are slightly translucent, and also they have almost a dreikanter 

 form. It is often stated that these Stanmore-Barnet gravels contain 

 quartzite : it is possible that some of the small pebbles from the 

 Lower Greensand may be quartzite, though apparently none have 

 been recorded. The material called ' quartzite,' which is not com- 

 mon, is sarsen, derived from the Reading Beds, and of local origin. 

 Thus, these gravels contain foreign material, often in great 

 quantity, but it is derived from the area beyond the Chalk escarp- 

 ment, not far removed, but neighbouring, and the pebbles may be 

 described as ' neighbouring.' 



Thus there are two types of gravel containing foreign material 

 to be dealt with : — 



(1) Those containing' far-travelled stones, and 



(2) Those containing' only ' neighbouring ' stones. 



In the latter, the local pebbles are nearly all Tertiary, mainly 

 from the Reading Beds ; fragments of flint are distinctly uncommon 

 in the Stanmore-Barnet area. 



The eastern occurrences on this Tertiary Ridge are all at approxi- 

 mately the same level, a little more than 400 feet above sea-level,, 

 and it was to these occurrences that Prof. Hughes referred, when 

 he claimed them as marine. So long as they remain at this 

 level, the quartz-pebbles are abundant, and the associated Reading 

 pebbles are on the whole comparatively small. But, on approach- 

 ing Stanmore Common, the gravels gradually attain a greater 

 elevation, at one point 500 feet. As the height above sea-level 

 increases, so does the size of the Reading pebbles : thus, when the 

 highest point is reached, these pebbles are, on the average, much 

 bigger than those at Barnet, and many of them still show the 

 original beach-hammering (noding) of the Reading pebbles. 



