“…The Top Rock is the name given by Chatwin & Withers (1908) to the hardground in the district northwest of Reading in the Thames valley that occurs in the Chalk at the upper limit of the Holaster planus Assemblage Zone. What has been taken to be the same hardground occurs throughout the Chilterns and extends northeastwards into Cambridgeshire (Brighton, 1928;White, 1932) and southern Norfolk (Hewitt, 1924(Hewitt, , 1935. Chatwin & Bromehead (1924) believed that they could also recognize the Top Rock in north Kent.…”