170 GEOLOGY: R. W. SAYLES 
if there must be a very strong probability of these being similar cases, 
in spite of the millions of years which separate the two glacial periods. 
In speaking of the banding it is not possible at this writing to say 
anything about the formation of slate under the main tillite. The band- 
ing in this slate appears to be somewhat different from the banding in 
the slate under discussion, but there has not yet been time to study it. 
It should show points of interest in regard to the climate responsible for 
the glacial advance, while the slate above the tillite should show the 
conditions responsible for the retreat. 
Evidence of seasons during Permian times has come from New South 
Wales, Australia, in the discovery of well marked annual rings of growth 
in trees of Permian Age.'* From Brazil similar evidence was obtained 
in tree trunks of the same age, and perhaps in the Triassic period which 
followed.^ Such findings, together with what now appears to be good 
evidence of seasonal changes at the locality which is now known as 
Boston, would make it appear that all these localities were in a tem- 
perate zone during Permian times as now. Furthermore, the close 
similarity between the layers in the Pleistocene glacial clays and the 
layers in the slate at Squantum would make it appear that the tem- 
peratures at the close of the Pleistocene and Permian were very similar. 
Not all slates which exhibit banding are of glacial origin, but a close 
study of the slate at Squantum should give certain definite criteria for 
the determination of glacial slates at other localities, and thus reveal 
facts hitherto unknown concerning the past climate of the earth. As 
glacial till is usually a land deposit and subject to rapid erosion, it is not 
likely to be preserved as tillite unless submerged beneath a body of 
water relatively soon after deposition. This is not true of a glacial 
slate, for slate originates in water and is thus very much more likely 
to be preserved than tillite. Hence, it follows that the discoveries of 
glacial slates should be more numerous than discoveries of tillites, and 
such discoveries may turn out to be as good evidences of glaciation as the 
tilHtes themselves. In this new way it may be possible to obtain very 
much more knowledge of past geological climates than we could ever 
obtain by the search for tillites alone. 
^R. W. Sayles, The Squantum tillite, Bulk Mus. Comp. ZooL, Harvard Univ., 46, 
No. 2, 141-175 (1914). 
2 Charles P. Berkey, Laminated Interglacial Clays of Grantsburg, Wisconsin, The 
Journal of Geology, 13, No. 1, 36-37. January-February, 1905. 
3 B. K. Emerson, The Geology of New Hampshire County, U. S. Geol. Surv. Monogr., 
29, 706 (1898). 
^ Shirley and Arber, Queensland, New South Wales, Bull. Geol. Surv., No. 7, 14 (1898). 
^ I. C. White, Relatorio final apresentado A S. Ex. o Sr. Dr. Lauro Severiano MUller, 
Comissao de estudias das minas de Carvao de Pedra de Brazil, Rio de Janeiro, 1908. 
(Printed in Portuguese and English.) 
