552 r. G. CLAPP GLACIAL PEEIOD IN NEW ENGLAND 



StricB of diverse directions. — In a discussion of the deflection of striae 

 in the vicinity'of Boston, Upham * shows that while the prevailing strike 

 of the glacial striae in Somerville and vicinity is south 20 to 30 degrees 

 east, the drumlins in the Boston basin are all aligned with their major 

 axes striking south 45 to 70 degrees east. A few fainter and shorter 

 cross-striffi strike, however, south 80 degrees east, south 30 degrees west, 

 and in other directions. Upham explains this discrepancy (page 41) by 

 the hypothesis that the drumlins were deposited near the close of the 

 glaciation (supposed by him to be Wisconsin), and that at that time the 

 ice was moving more eastwardly than during the time of greatest frigidity. 

 The fainter striae are explained by local divergence in the direction of the 

 ice during its later stages, when it was more dependent on the configura- 

 tion of the surface. 



Deflected striae have been observed by the present Avriter and other per- 

 sons at many points in Massachusetts and Maine, and are usually ex- 

 plained as Upham has explained those near Boston. The diverse strike 

 of the drumlins, however, can be as satisfactorily explained by the prob- 

 ability of their having been formed at a stage previous to that of most 

 abundant striae. If the principal strige are Wisconsin, the probable Mon- 

 tauk age of the drumlins would be corroborated, and some of the diverse 

 striae might be of Montauk age. A careful investigation of the directions 

 of striae and of the relative age of main and deflected striae throughout 

 the region would doubtless throw valuable light on this subject. 



As the present writer has not had time to fully investigate the matter 

 of strife in the field, he does not feel qualified to discuss it further. It 

 Avould seem important to compare the strike of drumlin axes with striae 

 found below drumlin till where it rests on bed-rock. 



WISCONSIN RETBEATAL DEPOSITS 



If tlie theory of glacial complexity be correct, the Wisconsin retreatal 

 deposits, as recognized in the new interpretation of phenomena, will 

 include the ordinary kames, moraines, eskers, sand plains, and irregular 

 deposits commonly grouj^ed under that class, with the following important 

 exceptions : 



In many cases deposits of till have been found overlying the above 

 mentioned types. It seems probable that only a part, and perhaps a very 

 small part, of the retreatal deposits hitherto classed as Wisconsin belong 

 in reality to that stage. It is believed that many of the irregularities 

 and hitherto inexplicable phenomena in the arrangement of sand plains 



* Proc. Boston Soc. Nat. ffist , vol. xxvi, 1805, pp. 3."?-42. 



