18 
FOX-STRAXGWAYS : GLACIAL PHENOMENA NEAR YORK. 
to the distribution of the glacial beds ; let us now see how tar the 
evidence in the neighbourhood of York bears out the supposition. 
It was one principle put forward by Professor Lewis " that every 
glacier at the time of its greatest extension is bounded and limited 
by a terminal moraine." This principle is well exemplified through- 
out Yorkshire, and perhaps nowhere better than near this city, 
where the moraine, which terminated what we may call the York 
Glacier, is situated. This moraine forms two more or less parallel 
mounds of boulder clay and gravel, which extend across the lower 
ground in a north-easterly directioji, the one from Y^ork, the other 
from Escrick. They form most striking features in the great plain 
of York, and are very conspicuous in the maps of the Geological 
Survey and in that accompanying the paper by Mr. Kendall. These 
ridges are between two and four miles apart, and rise to an elevation 
of about 50 feet above the flat country on either side. 
The main points insisted upon by Professor Lewis are in 
accordance with the observations made by the Geological Survey, 
and, I believe, are accepted by Mr. Kendall : but there are one or 
two statements made by the latter about which I should like to offer 
a few observations. In the first place, there appears to be a slight 
misunderstanding as to the exact meaning of the colours used on the 
official maps. The areas coloured blue are not entirely stiff boulder 
clay or till. They frequently contain sandy streaks and patches that 
are too small and irregular to map, and larger areas of gravelly drift 
that are too clayey to be considered a gravel. In these maps the 
distinct patches of sand and gravel are separated out, but the rest of 
the drift is thrown in with the boulder clay, and consequently the 
blue colour includes much that may be considered morainic. No 
distinction is made either between true boulder clay with erratics 
and local drift, so that it does not follow that all the areas coloured 
blue are true boulder clay."~ I have been induced to offer these 
remarks as some exception has been taken to the mapping of the 
drift in this district. 
Mr. Kendall, in alluding to the mounds at York and Escrick, 
* This applies to the drift in the southern portion of the Vale of Pickering 
and other places, which Mr. Kendall regards " with a good deal of suspicion." 
