The Geology of Newton

by James W. Skehan, S.J. and Catherine W. Barton

Glacial Geology

The youngest deposits within the Boston Basin region including Newton are of glacial origin (Fig. 4). There is a great variety of forms and types of such deposits. These consist generally of "hardpan" which was deposited directly where the rock fragments (till) fell out of the ice as it melted, or deposits which were formed under the ice (drumlins). Such drumlin deposits are elliptical in shape and their long axes show the direction of movement of the glacier. Such deposits are represented in Oak Hill, Bald Pate Hill and many others (Fig.4).

Another major land form and natural resource consists of layered glacial deposits which have been deposited by meltwater from the glacier. These esker deposits may have formed as crevasse fillings or as sub-glacial stream deposits. Such outwash deposits are found in Edmands Park, Waban, Auburndale, Newton Centre, Newtonville, and Cutler Park in Needham. Outwash plain deposits were laid down in front of the melting glacier by a meandering stream produced by the melting glacier.

Finally the alluvial deposits consist of post-glacial sediments developed in the 14,000 year period since the glacier receded from New England. Such sediments are swamp deposits including peat and certain stream deposits.

GEOLOGY FIELD TRIP

A series of nine field locations, or stops, has been chosen to facilitate firsthand study of examples of Newton's bedrock geology and the forms which glaciations has superimposed on and around the rock outcrops.

These stops are either on land in public ownership or are so located that permission to observe the formations will not be necessary. They are convenient for bus tours or for smaller group or individual visits.

Beginning at Stop 1 in Chestnut Hill, the stops follow a clockwise sequence westerly, then northerly, then easterly, and end up at the slate outcrop at the campus of the Newton College of the Sacred Heart.

STOP 1. HAMMOND POND RESERVATION

Access to parking lot is from Hammond Pond Parkway just off Boylston Street (Route 9).

Features to be seen:

1) Roxbury Conglomerate crops out throughout the Reservation. The conglomerate contains quartzite, granite and felsite pebbles which are rounded to sub-rounded in shape.

2) Outcrops of sandstone embedded in the conglomerate can be seen along the east side of Hammond Pond Parkway or along the bend in the main path in the Reservation.
       a) differences in grain size between the conglomerate and the sandstone.
       b) layering of the sandstone.

3) Jointing in the conglomerate (Fig. 5). In some locations it can be seen that the joints cut right through some of the pebbles as well as the matrix of the conglomerate.

4) Trees growing in joints in the conglomerate in the hemlock grove on the west side of the Reservation. As their roots grow larger, more and more pressure is applied to the rocks and eventually this pressure splits the rocks apart (Fig. 6).

5). On top of the large cliff at the entrance to the Reservation by Stearns parking lot, you may see glacial grooves and a perched glacial erratic (Fig. 7). Perched boulders can also be found in the formation around the hemlock grove.

6). Pieces of amygdaloidal lava can be found on the hill at the left of the MDC pathway as one goes toward Hammond Pond Parkway.

Webster Conservation Area (south)

West of Hammond Pond Parkway and south of the MBTA track. Park at Temple Mishkan Tefila.

1) This area is best known for its Roxbury Conglomerate fissure caves --known locally as Gooch's Caves.

2) Contacts of Roxbury conglomerate with sandstone can be found in the high formation about 400' north, of the Temple.

Webster Conservation Area (north)

West of Hammond Pond Parkway and north of the MBTA track. Off the southbound lane of the Parkway. Enter the pathway about 600' south of Beacon Street.

1) To the right of the path are thick sandstone ledges alternating with Roxbury Conglomerate. This large sandstone formation may be a sand bar deposited in a stream. Ripple marks such as are made by water may be seen.

2). Note very long, almost vertical joint toward the westerly end of the sandstone ledges. One of the best examples of a joint in Newton (Fig. 5).

Corner of Beacon Street and Bishopsgate Road

Park along Beacon Street or walk from the Webster Conservation Area. Note the sandstone beds contorted in tight "hairpin" folds. The sandstone slumped while the layers were still soft (Fig. 8).

 
 

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