Pleistocene stratigraphy of the Boston Harbor drumlins, Massachusetts

Evidence from the Boston Harbor drumlins indicates that two superposed tills were deposited during glacier advances which were separated by a long nonglacial interval. At Long and Peddocks Islands, argillans and truncated clay-filled fractures, along with discontinuities in clay-mineral composition, define the till contacts. Physical indicators separating the tills are not apparent at other exposures, where till boundaries were defined solely by discontinuities in clay-mineral composition. The weathering profile in the upper part of the lower till indicates extensive weathering under a climate similar to that of today, and probably similar to that of the Sangamon Interglaciation. The depth of the weathering profile, the sequence of clay-mineral alteration products, and the presence of pedogenic features in the upper part of the lower till are comparable to Sangamonian weathering profiles in the midwestern United States, implying that the lower till is Illinoian or older.