James Charles Clutterbuck, Agricultural Notes on Hertfordshire (1864)
“ The soil of the upper levels of the clay district marked by the rounded flint-pebbles embedded in the sand is wet and unkindly, not capable of bearing grass of any value, and ungrateful under the most liberal treatment as arable land. This gravel, with its characteristic blue-pebble, is transported in many cases below the higher levels, where the sterility of the soil is in proportion to the thickness of the bed. Where the London clay comes to the surface it forms a stubborn soil, which, however, by draining and a liberal treatment is made to grow abundant crops of grass. ”
