In a series of recent papers (Green & McGregor, 1978; McGregor & Green, 1978; Green, Hey & McGregor, 1980; Green, McGregor & Evans, 1982) the authors have sought to refine the stratigraphic scheme for the Lower and Middle Pleistocene depositional stages in the basin of the proto-Thames, using lithological features of the gravel deposits. In the Vale of St Albans , morphostratigraphic relationships , discernible further west in the middle Thames area (Hare , 1947), are weak. Terrace morphology has been severely degraded due to a combination of mass movement and periglacial activity associated with glacial phases , and particularly with the proximity of Anglian ice. An opportunity to test the sensitivity of a lithostratigraphic scheme in this area has been provided by the reconstruction of the Ml motorway between junction 5 (Watford) and junction 8 (HemeI Hempstead) in Hertfordshire (Fig. 1). Between these junctions, a continuous temporary section approximately 9 km in length was examined, and gravel was encountered in several separate outcrops. Samples were collected from each of the major outcrops, above the level of a low terrace of the River Colne , at those exposures which showed the least evidence of post-depositional disturbance. A profile drawn through the sample points runs almost orthogonally to the axis of the Vale of St Albans. The profile (Fig. 2) shows that the samples are arranged in a vertical sequence which can be related to the approximate altitudinal limits of the main pre-Anglian depositional stages in this area (Gre en, McGregor & Evans , 1982, fig. 3). These are, the Higher Pebble Gravels, Westland Green Gravel , Higher Gra vel Train and Lower Gravel Train stages . Below the Higher Pebble Gravels , these stages are thought by the present authors to represent evidence of pre-Anglian glaciations in the upper catchment of the proto-Thames. In addition, distinctive gravels are found in association with chalky tills of Anglian age and have been treated by the present authors as Anglian glacial gravels. These are either preglacial gravels reworked by outwa sh of the ice advance or meltwater gravels related to ice decay.