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56 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
rippled (the ripples indicating a current from the North) and having occasional thin beds of 
shale interstratified.”” BLANFORD, ET AL., 1859, p. 51. 
Farther on (loc. cit., p. 53) Blanford writes: 
“Tf the deposit of shale were thick, it might resist disturbing action, and after a certain 
period, during a gradual depression, a regular alternation of bands of shale and sandstone 
might be produced, such as is frequently seen in the beds in question.” 
As this Talchir tillite is only 20° north of the equator it has always been 
one of the greatest stumbling blocks to the theorists who have attempted to 
explain the cause or causes of Glacial periods. If the banding noted by Blanford 
is really due to seasonal changes and deposition, it will be necessary now to 
explain not only the former presence of the great ice sheet in the Tropics but 
marked alternations of seasons also. The state of mind of geologists in regard 
to the difficulties in explaining the Permo-Carboniferous glaciation was well 
expressed by Prof. James Geikie in a letter to me. He wrote January 1911: 
“The problem of the Permian or Permo-Carboniferous glacial period is a hard one. It 
would seem to have been even more excessive than that of Post-tertiary times, and no expla- 
nation of its cause hitherto advanced seems to me at all satisfactory.” 
In the Permo-Carboniferous glacial beds at Bacchus Marsh a short distance 
north of Melbourne, Australia, there are some stratified mudstones which, 
from the description, appear to resemble in one respect at least the slate under 
the tillite at Squantum. A description by Officer and Hogg reads in part as 
follows: 
“ Stratified mudstones. The beds are first described, as they form the lowest of the 
glacial series visible in our district. They consist of regularly stratified deposits of a more or 
less hard tenacious clay; they are occasionally finely laminated; they vary somewhat in 
colour, blue and yellow being the prevailing tints.” Orricer anp Hoae, 1898, p. 181. 
It is apparent that these mudstones show banding and the alternations of 
color spoken of strengthens this view. 
An earlier description of these same mudstones reveals contortions similar 
to those in the Squantum lower slate. I quote Sweet and Brittlebank as 
follows: 
“ As has been before remarked, the mudstones, conglomerates, and sandstones alternate 
with each other in repeated succession — now in thick beds, now in thin beds, now highly 
laminated, then for short distances disturbed and distorted, with the stratification obscured, 
and this is repeated over several miles of country in the direction of the dip as well as along ~ 
the strike.’ Swrerr AnD BriITTLEBANK, 1894, p. 384, 385. 
