Dr. D. Woolacott—The Interglacial Problem. 67 
formation of the raised beaches), alluvial and land deposits, and 
are thus partly formed of thick deposits of reassorted glacial and 
other material. The leafy clays were deposited in tranquil con- 
ditions, and while they are usually regarded as glacier-lake deposits 
some of them may also be of estuarine origin. Merrick has found 
in these finely laminated clays numerous tracks of some forms of 
locomotive invertebrate life,! probably of annelids, as no fossils 
have ever been found in them, but some of the tracks are like those 
of crustacea or gastropods. 
The sequence worked out by Merrick includes :— 
Soil. 
Yellow clay (weathers into short columns, prismatic clay). 
Brown clay (stiff brown clay with boulders). 
Rotten loam sand. 
Common clay (roughly bedded boulder-clay). 
Surface leafy clay. 
Black clay (with striated and unstriated boulders). 
Leafy blue clay. 
Scarp (boulder-clay). 
Sand. 
Similar leafy and other clays are found in the Tees valley.? 
Sometimes in the leafy clays boulders are found, which would 
appear to have been rafted by ice or vegetation and dropped into 
the deposit.® 
The distribution of most of the rock-fragments in the Superficial 
Deposits of Northumberland and Durham can be explained from 
the general trend of the ice-movements in the area, but that of some 
rocks, such as Flint, Chalk, and Magnesian Limestone, is so peculiar 
as to be worthy of special notice. While many of the positions in 
which pieces of these rocks occur offer no special difficulty some 
undoubtedly do, if we accept the hypothesis that the Chalk and the 
Flint were brought by the Scandinavian ice from the bed of the 
North Sea, and, in connexion with the distribution of the Magnesian 
Limestone, that the direction of ice-movement down the 
Northumberland coast was always from north to south. Flint 
occurs in the Scandinavian Drift at Warren House Gill, and in a 
comparatively stoneless clay resting on the boulder-clay at Trow 
Rocks, South Shields, and at Tynemouth (Howse’s Scandinavian 
Drift). I have never seen it in, and I do not remember it having 
been recorded from the typical Main or British Boulder-clay in 
Northumberland and Durham, but it may occur. It is present in 
the deposits at Horsebridge Head, and at the Lyne Burn already 
noticed. It has been found in the Kaims and large rolled flints occur 
in the gravels and sands at Cleadon (Raised Beach). The late 
1 See photographs op. jam cit., pl. i. 
2 Trechmann, op. jam cit., 1920, p. 192. 
3 See description of such a boulder by Professor Lebour, Proc. Univ. Durham 
Phil. Soc., vol. ii, pt. 1, 1901-2, p. $1. 
