426 
CLARK : GLACIAL SECTION'S. 
There must also have been corresponding- depressions of the 
old surface ; for brick fields W. of the Heworth road are worked 
to a depth of 20 feet or more. This is a good example of the level- 
ling nature of the brick-clays, to which allusion has previously 
been made. 
The largest boulder seen in this part was a block of sand- 
stone, measuring 2-^x2x1^ feet, containing about 3| cubic 
feet, and therefore weighing at least 5001b. 
Gravels are worked, as has been said, on both banks of the 
river ; their nature and position showing that they are rearranged 
glacial beds. The stones are identical, some of them retain their 
ice-marks, and the passage downwards into the true glacial beds 
is imperceptible. In the very midst of boulder clays (as in photo. 
VI,* for example) occur gravel beds which cannot be distinguished 
from these, both consisting of more or less irregular deposits of 
boulders, pebbles, gravels, grit, and layers of pure sand, the latter 
often very much false-bedded. 
Gravel pits have long been worked between the road this side 
of Fulford new church and the river. They generally present a 
section 15 to 30 feet in height. The most peculiar feature 
is a bed of Manganese, 25 feet below the surface at the point 
worked in 1877. It was exposed at two positions 100 yards 
apart. The bed containing it consisted of loose dry pebbles, and 
was one foot thick. The upper five inches looked as if encrusted 
with soot (Mangarese dioxide, Mn. 0 2 ), whilst the pebbles beneath 
were brown with the sesqui-oxide, Mn 2 0 3 . This also appeared 
in the bed above, as much as 5 feet being affected in places. 
Below this iron gave a corresponding ochreous coating, although 
the matrix was clayey. The workmen said they met the " soot " 
in all parts, although it occasionally thinned out. Samples of it, 
sifted to free from coarse sand, Were analysed by Mr. T. H. 
* See Plate ii., Fig. 3, left (S.W.) end. Copies of 8 Photos, cabinet size, 
maj be had through the author. They arc referred to and described 
later on. 
