CONTEMPORANEOUS DEFORMATION: A CRITERION 

 FOR AQUEO-GLACIAL SEDIMENTATION 



FREDERIC H. LAHEE 

 Massachusetts Institute of Technology 



Previous records of deformation in unconsolidated strata. — • 

 Deformation in unconsolidated strata has been observed and 

 recorded by many writers on geological subjects. Faults having 

 a displacement ranging from a fraction of an inch to a few feet are 

 often seen in sections of glacial sandplains, eskers and kames, and 

 in river terrace deposits.^ Being due probably to removal of some 

 lateral or subjacent supporting material, these faults are nearly 

 always of the normal type. Folds in unconsolidated sediments 

 are of much less common occurrence. J. B. Wjoodworth has fig- 

 ured and described such deformation in the kame gravels west of 

 Fresh Pond, in Cambridge, Massachusetts.^ These folds, having a 

 height of as much as lo feet, were overturned southward in a way 

 to indicate that they had been formed by the thrust of a readvan- 

 cing ice lobe. The same features were described a few years earlier 

 by Woodworth and Marbut.^ Similarly, contortion in the Colum- 

 bia formation on Martha's Vineyard and Block Island has been 

 ascribed to the pressure exerted by overriding Pleistocene ice.'' 



In all the instances noted above the deformation was in no way 

 associated with the deposition of the beds. It was distinctly subse- 

 quent in point of origin. In the pages that follow is described a 



' The present writer described one good example of this phenomenon several 

 years ago {Science [IV], XXVIII [1908], 654). 



2 Essex Institute Bull, XXIX (1898), 71. 



3 U.S. Geol. Survey, Ann. Rept. 17 (1896), Pt. i, p. 990. 



4 J. B. Woodworth, "Unconformities of Martha's Vineyard and of Block Island," 

 Bull. Geol. Soc. Am., VIII (1897), 197-212; "Glacial Origin of Older Pleistocene in 

 Gay Head Clii5s ....," ibid., XI (1900), pp. 455-60. Shaler, at an earlier date, 

 believed these folds were of orogenic origin. See, e.g., his "Report on the Geology 

 of Martha's Vineyard," U.S. Geol. Survey, Ann. Rept. 7 (1888), p. 345; and his "Ter- 

 tiary and Cretaceous Deposits of Eastern Massachusetts," Bull. Geol. Soc. Am., I 



(1890), 446-47- 



786 



