46 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
beds of fine conglomerate and slate laminae was. a bed of tillite intercalated in 
the slate with rounded, angular, and subangular rock-fragments of sizes up to 
one foot in diameter embedded at all angles. Above this tillite bed was lami- 
nated slate, and some beds of conglomerate, one of them being as much as eigh- 
teen inches thick. Thinner beds of conglomerate alternating with laminated 
slate followed for about ten feet and then very regularly banded slate appeared 
of dark and light tints of red. From the description given it is evident that the 
ice retreated an indefinite distance but not very far, then advanced again as 
evidenced by the tillite bed in the slate. A retreat was again inaugurated and 
coarse beds of conglomerate alternating with beds of fine sediment followed. 
Finally the ice retreated to some distance and regular layers of fine sediment 
alternating with layers of slightly coarser sediment were laid down. About 
forty feet above the lowest of these regular banded slate layers, appeared another 
bed of tillite, about four feet thick, intercalated in the slate. As in the first 
bed, there were rounded, angular and subangular rock-fragments, and in addition, 
a large lump of slate and similar smaller lumps much contorted, the whole mass 
without any trace of stratification and the included fragments lying at all angles. 
The upper and lower contacts with the regularly banded slate were very uneven. 
It appeared that the ice ploughed up the clay and dragged upward into the till 
the lumps described. (Sayles, 1914, p. 154, 155). As already stated the band- 
ing above and below this last tillite bed has a very even interval. (See Plates 
5 and 8). For the next fifty feet upward in this deposit, the slate exhibited 
very even banding but occasional sandy layers and contorted zones showed 
that the ice had not withdrawn to a great distance. At many places there 
were zones of folding and distortion, and in most of these zones small pebbles 
were included among the folded layers. (See Plate 8, fig. 2). These zones 
of folding gradually vanished and the occasional sandy layers also vanished, 
so that nothing but the dark and light red bands of slate could be seen. It 
appeared that these dark and light bands might mean finer and coarser sediment 
and a subsequent examination of thin sections proved this to be the case. Pro- 
gressing upward the bands became gradually thinner until the exposure came 
to an end just north of the viaduct. There is a break in the slate series here 
between outcrops of about 150 yards. South of the viaduct and by the side 
of a huge Pleistocene boulder of Roxbury conglomerate, there was another 
slate outcrop with banding somewhat finer than on the north of the viaduct. 
What has happened between these outcrops in the structural relations of the . 
slate it is difficult to say. There was another break in the observations, of 
