The Geology of Newton

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

STOP 4. OUTCROPS ALONG NAHANTON STREET ACROSS FROM THE CHARLES RIVER GOLF COURSE AND FARTHER WEST AT THE KENDRICK STREET BRIDGE OVER THE CHARLES RIVER

The outcrops are road cuts. Parking is difficult. The rock consists of the Brighton Volcanics.

1) Excellent examples of mineralization. Well formed crystals can be seen. Please do not remove crystals.

2) Minerals which can be found in veins are:
Chlorite
Quartz
Calcite
Pyrite/Chalcopyrite
Hematite

3) Small fragments of red felsite are present in the rock.

4) Differential weathering.

5. HEMLOCK GORGE MDC RESERVATION AT NEWTON UPPER FALLS

Access to the west (Needham) side of the Charles River at the Gorge from Route 9 eastbound lane is by turning right at Ellis Street and proceeding to the signal at Chestnut Street-Elliot Street intersection. Turn right onto Elliot Street. Cross bridge over the river. Turn right onto Reservoir Street and park at the Sudbury Aqueduct pathway which leads to the famous Echo Bridge over the river.

To the left of the aqueduct path is a large outcrop of boulder conglomerate. Notice that the pebbles in the conglomerate are stretched (Fig. 9).

Nearer the level of the River is a cave formed by running water.

Other features to be noticed:

1) Erosion of the Gorge by running water.

2) Boulders up to 1 foot long in the conglomerate.

3) Development of close-spaced mineralized fault fractures in pebbles and boulders indicative of a fault zone nearby.

Access to the east (Newton) side of the Charles River is from Ellis Street. Two or three cars can be parked on the Reservation below the Echo Bridge abutments. Walk down toward the ramp leading off Route 9. Circular dam just below Route 9 viaduct. A dike of basalt can be seen above the Circular dam. The dike has microscopic vugs in it. On the north side of Route 9 on the Wellesley side of the Gorge is an intrusive contact of basalt into conglomerate. The southernmost building of Wellesley Office Park is located just above this feature.

Sullivan Avenue at Elliot Street, Newton Upper Falls Walk a short distance from Hemlock Gorge up Sullivan Avenue from Elliot Street and observe at the right in a conglomerate cliff, half of a pothole formed as smaller pebbles were rotated in a weak spot in the conglomerate by swiftly flowing water when the gorge was being cut.

STOP 6. ROCKY MOUNTAIN --LARGE OUTCROP OVERLOOKING ROUTE 128

The rock is composed of the Brighton Volcanics. Park at the Recreation Road bridge over the Charles River along the spur from northbound Route 128 which leads to the Massachusetts Turnpike entrance and to Route 30. Walk south to the railroad overpass over Route 128. This railroad spur is all but abandoned. Climb the hill to the left of the railroad.

Notice:

1) Glacial grooves and striae at the top of the outcrop. The rock has been glacially polished at the left of the path leading to the summit. Amygdules which are now filled with epidote and calcite can be seen at the summit.

2) "Roche moutonnee" features, caused by glacial plucking at the south side of the hill and polishing of the rock surfaces on the hill may be observed.

3) The Auburndale Esker can be seen to the east behind the Grove Street apartment development (Fig. 10). The Grove Street Hills formerly occupied the present site of the Woodland Golf Course. They were excavated during the 19th Century for fill in the Back Bay area of Boston.

4) The fault-line marking the western border of the Boston Basin can be discerned to the northwest above the Massachusetts Turnpike Tollgate and below the red roofed Wachusett Reservoir control station in Weston just west of Route 128.

5) Some mineralization is apparent in tension gashes and veins.

6) The blue and purple color of the Brighton Volcanics which form Rocky Mountain.

7) On the southern end of the summit, look for examples of the difference between quartz and calcite crystals. The calcite crystals have been weathered more since they are soluble in water whereas the quartz crystals are not.

8) Look for a pink feldspar-bearing vein on the side of the summit toward the MBTA terminal.

9) There is a single porphyry rock at the left of the path on the first rise toward the summit. Feldspar crystals are embedded in the matrix.

STOP 7. CLAFLIN SCHOOL

On Lowell Avenue north of Commonwealth Avenue and south of Hull Street. The school is well above street level on a rocky bank. The face of the bank below the school shows a fine display of glacial scratches, grooves, and chattermarks (Fig. 11). The parking lot at the rear of the school is on the site of a former quarry cut into the Brighton Volcanics.

STOP 8. EDMANDS PARK

A small esker can be seen to the right as you enter the park from Blake Street. A trail leads back into the park (Fig. 13) and then along the top of the esker. Note the sandy soil and the steep sides of the esker as you walk along its "back".

STOP 9. NEWTON COLLEGE OF THE SACRED HEART

A small isolated, conspicuous outcrop of laminated Cambridge slate can be seen on a large lawn close to the driveway off Colby Street (Fig. 12).

Notice the strike and dip of the outcrop. There is also a very small fault which can be seen in the northeast edge of the outcrop, offsetting layers formerly continuous.

This kind of slate is found elsewhere in a number of places in northern New England. A similar slaty ledge has been observed behind a house at Annawan Road and at 59 Tamworth Road both in the Waban section of Newton.

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