102 



BULLETIN OF THE ESSEX INSTITUTE. 



same side of the pond has been frequently observed in 

 the heads of clay which protrude into the overlying grav- 

 els. These masses sometimes rise up as much as ten feet 

 above the level of the pond. In one part of the section 

 a bed of clay was forced up with the gravels into a broad 

 arch as shown in a recent report on the Cambridge 

 clays.' 



The frontal wash-plain has an average elevation of about 

 thirty feet above sea-level. It is pitted by broad shallow 

 depressions most of which have disappeared under the 

 extension of streets and buildings and through the action 



Fig. 6. Section (now destroyed) on west side of Fresli Pond, as seen June 7, 

 1891, sliowing folded and eroded gravels. Tlie arrow indicates direction of ice 

 motion. Elevation in feet. 



of peat-making plants. One such peat-bed was encoun- 

 tered in laying the foundation of the botanical section of 

 the University Museum on Oxford street. 



Several glacial deposits of an earlier date than the 

 plain interrupt its extent. The knoll of till in Harvard 

 College yard, extending to Dana Hill, is such a mass, as 

 are also the partially graded kames in Mt. Auburn ceme- 

 tery. There are no contemporaneous kames or eskers 

 associated with the plain. It appears to have developed 

 largely as overwash and outwash from the moraine before 

 mentioned. The cuts in the plain formerly exposed in 



> See Shaler, Woodworth and Marbut; IVtli Annual Report, U. S. Geol. Survey, 

 pt. i, p. iteo. Jig. 37. 



