Professor G. W. White congratulated the speaker on his important contribution. The surface features Dr Boulton described from the Arctic were similar to those he and his associates had studied in late Pleistocene (Wisconsinan) deposits of the northern Great Plains of Saskatchewan, Alberta, North Dakota and in the Allegheny Plateau in Ohio and Pennsylvania. The internal structures of many Pleistocene deposits could be explained by the principles so well set forth by the speaker. Till masses in Kame gravels are precisely like the 'mudflows' described, and do not indicate glacial readvance.

Till sheets that are separated by a palaeosol upon the lower one, however, must be interpreted as deposits of separate ice advances, separated by a length of time sufficient for soil formation. Variations in structure within each till sheet can be explained by the 'Boulton hypothesis'.

The recognition of structural and compositional differences within till and other glacial deposits, as illustrated, is of importance to engineers designing excavations, tunnels, foundations, water supply and waste disposal projects. If the lateral and vertical variation in density, permeability and other engineering parameters is not recognized, unexpected problems may arise. Professor White hoped that Dr Boulton would find it possible to deal with such geotechnical application of his findings in some future paper.

The Author thanked Professor White for his remarks and was encouraged to hear that interpretations such as he had just outlined could be applied to many North American sequences.

On the question of palaeosols, he agreed with Professor White, but

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