MANSFIELD: ROXBURY CONGLOMERATE. 131. 
of material worked over from the till sheet that once covered the 
region. At one locality a morainal ridge (Woodworth, e, p. 34) is 
composed altogether of blocks and cobbles of Potsdam sandstone. 
On the crest and western or landward side the blocks are still prevail- 
ingly angular. On the eastern or wave-washed slope the blocks are 
often well rounded, particularly at the lower levels. “The fragments 
decrease in size from the crest and near the 600 foot level are coarse 
gravels. The large blocks are between three and four feet in length, 
but blocks yet longer occur. Ovoid masses of this size in the upper 
zone of beach action attest the strength of the waves.” At a second 
locality, a low, modified hill about two miles northwest of Mooers 
Junction, rolled and rounded pebbles appear on the west slope. “The 
underlying glacial materials are the angular rock fragments peculiar 
to glacial till. It is evident that long continued and effective wave 
action took place on the west slope of this hill” (ibid., p. 40-41). The 
rounding of the glacial fragments in these shore lines, together with 
the sorting of the materials at the first locality indicate the character 
of the changes produced by either lacustrine or marine wave action 
upon unsorted glacial debris. The longer such processes are con- 
tinued the more perfect become the shaping and sorting of the mate- 
rials, until all traces of glacial action are removed. In the Champlain 
valley the lacustrine and marine stages at which the shore lines were 
built must have been of relatively short duration, for not only are the 
glacial deposits only slightly modified but in some instances the beaches 
are seen to rest on glaciated surfaces (ibid., p. 33). 
The intimate association of fluviatile action with glacial action has 
already been noted. The materials swept from a glacier by torrents 
of ice water soon lose their distinctive shape and markings unless 
deposited before they travel far. The ordinary stream washed glacial 
materials along the northern side of the Alps are described by Penck 
(Penck et al., p. 8) as worn, rolled, rounded, and deposited like the 
pebbles of a water course. They are characterized, he says, by their 
horizontal stratification or by an alternation of horizontal and in- 
clined layers. Upstream the alluvial deposits become larger and more 
angular, the stratification becomes less regular, striated pebbles appear 
and the formation becomes truly glacial. Between the unmodified 
glacial material and the undoubted “Auvio-glacial” deposits is a 
transition zone characterized by a morainic phase of the alluvium, 
and by the presence of blocks or of occasional striated pebbles. The 
““fluvio-glacial” material rests against the actual glacial debris, and 
forms a vast inclined plane descending from the moraines and forming 
