TRANSPORTATION BY ICE 265 



tonnces. Combined erosion by glaciers and subglacial streams is 

 called fluvioglacial erosion. 



Transportation by Ice. As already noted, much material may 

 be transported by floating icebergs or floes and so become incor- 

 porated in marine sediments. Land ice transports rock debris on its 

 surface as superglacial drift, within its mass as englacial drift, and 

 at its bottom as subglacial drift. In form the superglacial material 

 generally constitutes lateral and median moraines. (See postea 

 Chapter XII.) The englacial is likely to be scattered, and the sub- 

 glacial is often in the form of a more or less continuous sheet. 

 Changes from one position to another are constantly effected, the 

 subglacial rising by shearing and upward currents to become en- 

 glacial or superglacial, the englacial becoming subglacial by basal 

 melting of the ice or superglacial by surface ablation, and the super- 

 glacial material becoming englacial or subglacial through the action 

 of descending currents or by falling through fissures or crevasses. 

 By melting on reaching the sea this material may be incorporated 

 with marine sediments, or by advancing over forests and swamps it 

 may be deposited on organic accumulations (future coal beds), and 

 finally, by taking up material from the bottom of the shallow sea 

 over which it passes, the ice may incorporate remains of marine 

 organisms in continental sediments, as in the case of the fossils of 

 Tertiary or younger age included in the drumlins of Boston Harbor 

 and the moraine of Cape Cod. (Crosby and Ballard-13, Crosby-ii.) 



BIBLIOGRAPHY V. 



1. AIRY, G. B. Tides and Waves. Encyclopedia Metropolitana. 



2. ANDRESEN, C. C. 1861. Om Klitformationen og Klittens Behandling og 



Bestyrelse Kjobenhavn. 



3. BEARDMORE. 1872. Manual of Hydrology. London. 



4. BERKEY, C. P. 1913. Private Communication. 



5. BLACKWELL, J. E. Report on the Referees' Report upon the main 



drainage of the Metropolis (cited by Beardmore). 



6. BUCHANAN, J. Y. 1888. The Exploration of the Gulf of Guinea. Scot- 



tish Geographic Magazine, Vol. IV, pp. 177-200; 232-251. 



7. CARNEY, FRANK. 1910. Glacial erosion on Kelley's Island. Bulletin 



of the Geological Society of America, Vol. XX, pp. 640-645, pis. 108-110. 



8. CHAMBERLIN, T. C. 1884. The Requisite and Quahfying Conditions 



of Artesian Wells. U. S. Geological Survey, 5th Annual Report, pp. 

 131-180, 1883-84. 



9. CHAMBERLIN, T. C, and SALISBURY, R. 1906. Geology, Vol. i. 



New York, Henry Holt & Co. 



10. CORNISH, VAUGHAN. 1910. Waves of the Sea and Other Waves. 



London. 



11. CROSBY, W. O. 1879. Fossiliferous Boulders in the Drift of Truro. 



Proceedings of the Boston Society of Natural History, Vol. XX, pp. 

 136-140. 



