MANSFIELD: ROXBURY CONGLOMERATE. 129 
later determinations, is 1,427 feet (ibid., p. 297). The extent of the 
glaciated area in Australia is from latitude 42° S in Tasmania to 26° 
31’ S in Queensland and from 137° 30° E longitude to 151° 31’ E 
longitude (ibid., p. 300). 
:— South Africa. A considerable literature has already ap- 
peared with reference to the nature and origin of the Dwyka Con- 
glomerate, which forms the base of the Karoo system and overlies 
unconformably sandstones and shales that have Devonian affinities. 
The most recent publications that have come within the notice of 
the writer are by Mellor, Rogers, and Emmons. ‘The last gives a 
general summary of the literature up to 1896. As described by 
Rogers, the rock is usually bluish or green, compact and fine 
grained, composed of quartz and microcline, with a small quantity 
of other feldspars, epidote, garnet, calcite, and other minerals em- 
bedded in mud (A. W. Rogers, p. 147). The mud contains a vast 
number of boulders and pebbles of a great variety of rocks, scattered 
irregularly through the conglomerate without any arrangement in 
beds. There are many rounded boulders but there are also many 
flattened on one or more sides, with scratches of various depths, gen- 
erally in two or more directions (ibid., p. 142). In all respects these 
boulders and pebbles are similar in form and in the nature of stria- 
tion to those found among the glacial formations of northern Europe 
and America (ibid., p. 150). Some pebbles attain a diameter of ten 
feet (ibid., p. 167). 
The upper portions of the formation (Mellor, p. 685) are “locally 
associated with beds of massive sandstone and lenticular patches of 
cream colored shales and mudstones, which appear to have been 
deposited in pockets in the conglomerate and to consist of the finest 
glacial mud. The laminae are readily separable; they are smooth 
and similar in appearance and color to lithographic limestone or they 
are covered with delicate ripple-marks, as many as forty in the space 
of one inch.” The underlying surface gives clear evidence of the 
direction of ice movement, from north southwards. The striae main- 
tain a constant direction over large areas (ibid., p. 688). From the 
statements of Molengraaf and Rogers it would appear that the strati- 
fied portions of the conglomerate are not so local in their occurrence 
. as is perhaps implied in Mellor’s description. Molengraaf speaks 
(p. 260) of the unstratified mass as alternating with stratified beds 
which sometimes contain many boulders and pebbles. Rogers states 
(p. 154) that it is justifiable to regard those portions of the conglomerate 
that rest upon a striated floor as terminal or ground moraines, but 
that it is uncertain whether the whole of the conglomerate in the region 
