438 
CLARK : GLACIAL SECTIONS. 
Few boulders, except the limestone and lake-stones, retain 
the scratches. The former, when freshly removed, often had a 
beautiful polish, soon lost on exposure, a large mass, in my 
possession, weighing 42 pounds, shows as well the original 
surface with spar, and glacial fracture. 
The glacial beds here described most resemble the Purple 
Boulder Clays of Messrs. Searles V. Wood and Harmer. Their 
appearance, however, indicates a deposition from floating ice, 
rather than, or as well as from the moraine prqfonde of an ice- 
sheet. Otherwise it would be hard to account for beds of gravels, 
boulders, and current-bedded sands so closely associated with the 
tough stony clays. Judging from the material, the ice-sheet or 
floes must have come chiefly from the N.W. ; though even in the 
boulder clay specimens occur showing drift from the E. or N.E. 
There are many indications of a division into two glacial 
periods, the second much less severe than the first. To it might 
be assigned: — (1) the upper eastern deposits at the Poppleton 
Junction ; (2) the lenticular sand masses in the Heworth part of 
the Foss Islands Railway ; (3) Sand-beds D and E, and parts 
above, and to the S. of E in the Retreat section ; (4) the gravel 
bed of Photo. VI., and the bed to the S. W. of it in the plan of the 
new Goods Station area ; (5) the beds above the line shown in 
Photo. VIII., and continued on to the W. ; (6) the gravels, bould- 
ers and false -bedded sands in the upper part of the section behind 
the Passenger Station. 
Post-glacial beds, probably derived very directly from the 
glacial of the district, have been formed to a considerable depth. 
Brick-clays as well as gravel beds are worked for 30 feet or 
more. The river deposits seem to go much deeper, and the peat 
bed at Brett's brewery may be as easily explained if post glacial 
as if we call it interglacial. The beds above it partake more of 
the latter aspect. 
The Ouse as was pointed out many years ago, is 60 or 70 
feet above its preglacial bed. The slight protrusions from the 
