With this race is also associated by many authors (Schwalbe, Schliz, Klaatsch, Keith) the Galley Hill skull, which was found in 1888, buried at a depth of 8 feet in the 'high terrace' gravels 90 feet above the Thames.(49) Sollas thinks it highly probable that the remains were in a natural position and of the same age as the high-level gravels and the Palæolithic flints and remains of extinct animals which they contained, but Evans and Dawkins regard the Galley Hill man as belonging to a long-headed Neolithic race interred in a Palæolithic stratum. The gravels of the 'high terrace' in which the Galley Hill skull was buried are by no means of the geologic antiquity of 200,000 years assigned to them by Keith;(50) they are probably of Fourth Glacial or of Postglacial age, and lie within the estimates of Postglacial time, namely, from 20,000 to 40,000 years. The antiquity of the Galley Hill cranial type has been maintained with ability by Keith. The skull is extremely long or hyperdolichocephalic, the cephalic index being estimated by Keith at 69 per cent;(51) the brain capacity is estimated at between 1,350 c.cm. and 1,400 c.cm.; the cheek-bones are not preserved, so that no judgment can be formed as to this most distinctive character of the Crô-Magnon race. With this Galley Hill race Keith also compares the Combe-Capelle, or Aurignacian man of Klaatsch,(52) although he mistakenly considers the Combe-Capelle man of much less geologic antiquity. He continues: "Thus, while the writer is inclined to agree in provisionally assigning the Combe-Capelle man to the Galley Hill race, he believes that further discoveries will show that the Combe-Capelle man belongs to a branch marked with certain negroid features." SOLUTREAN FLINT INDUSTRY The 'Solutrean retouch' marks one of the most notable advances in the technique of flint working; it is altogether distinct from the 'Aurignacian retouch,' which is an heritage from the Mousterian.(53) The flint is chipped off by _pressure_ in _fine, thin flakes_ from the entire surface of the implement, to which in its perfected form the craftsman can give a thin, sharp edge and perfect symmetry. This is a great advance on the abrupt Aurignacian retouch, in which the flint is chipped back at a rather blunt angle to make a sharp edge. According to de Mortillet, the Solutrean method of pressure made possible the execution of much more delicate work.