MANSFIELD: ROXBURY CONGLOMERATE. 115 
but the beds generally shade off into each other and are not continuous 
for any distance. The rock exposures separately or in relation to each 
other exhibit all those characters that may now be seen in the great 
gravel fans of western and central Asia described above (Oldham, b, 
p. 464). The striations on the included fragments were thought by 
Oldham to have been produced by glacial action (ibid., p. 470) but 
King refers to the alleged glaciated pebbles as slickensided and states 
that the slickensides occur inside and outside the fragments and in 
the matrix (King, p. 127). 
The origin and source of the Bunter conglomerates of the Midlands 
and South Devon have been the subject of some controversy. Bonney 
describes the Bunter group as consisting of two wedge-shaped masses 
of sand separated by similarly shaped beds of pebbles (Bonney, b, p. 
370). There is some uncertainty whether they are of lacustrine or of 
fluviatile origin but he thinks they are probably the latter (ibid., p. 
371). The thick ends of the wedge-like masses point ‘northwest, 
indicating a source in that direction; but the gradation in size of the 
included fragments does not agree with that interpretation. The 
sands of the Bunter group are often false-bedded and occasionally 
contain well-rolled grains, suggestive of wind action (ibid., p. 373). 
In a later paper Bonney states that the beds in question are very unlike 
marine deposits, differing most of all in being at once widespread and 
thick and so not resembling any shingle beds of which he has knowl- 
edge (c, p. 295). Shrubsole describes the pebble beds at Budleigh 
Salterton in South Devon as consisting of pebbles which lie with their 
long axes at all angles and not at the angle of rest. The pebbles vary 
in size from one-half to one inch in length and are not sorted. The 
shape is variable,— longer than broad, broader than thick, and sub- 
angular. The evidence does not support the view of the early 
observers who regarded the pebble bed as a marine beach (Shrubsole, 
p- 315). 
——:— The United States. The High Plateaus of Utah, described 
by Dutton, furnish a remarkable example of extensive conglomeratic 
deposits ascribed to fluviatile action. The rocks attain a thickness 
of 2,000 feet over an area of 2,000 square miles (Dutton, p. 69). The 
fragments range in size from mere grains to blocks weighing several 
tons. Both fragments and matrix consist of voleanic materials with- 
out the admixture of debris from ordinary sedimentary or metamorphic 
rocks (ibid., p. 74). None of the fragments exhibit the sharp edges 
of fresh fracture. While well-rounded fragments are uncommon, it 
is not certain that any noticeable portion of them is absolutely free 
