Guide

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Glacial striations on Massachusetts bedrock ledges

April to November

Some bare rock ledges in Massachusetts carry fine parallel scratches and shallow grooves, cut by stones frozen into the bottom of an ice sheet as it slid over the rock. The lines record which way the ice moved: around Boston and across the central Massachusetts uplands, mostly toward the south-southeast.

Why this time of year

The scratches are on the rock in every season, so any snow-free month works. Bare ledges on hilltops and along trails are good places to look.

How to notice it

  1. Where a marked trail crosses bare rock ledge, look for fine straight scratches or shallow grooves that all run parallel, in the same direction.
  2. Notice which way the lines point. Around Boston and in the central Massachusetts uplands most run roughly north-northwest to south-southeast, though geologists have mapped southwest-trending scratches in places too.
  3. If a smooth ledge shows no scratches, that is normal. Weathering wipes many of them away and some rock never held them, so try another bare ledge.
  4. Check for a second set of lines crossing the first at an angle. Geologists read crossing sets as ice that moved in a different direction at another time.

Try this with kids: Lay a stick along the scratches. Which way does it point?

Word to know: “Striations”: fine parallel scratches cut into bedrock by stones frozen into the bottom of a moving glacier.

Safety

  • Bare rock is very slippery when wet or icy, so stay off sloping ledges in wet or winter weather.
  • Stay on marked trails, which also helps you avoid poison ivy and ticks.

Sources

  • home.nps.govNPS (federal, primary for the general mechanism; examples are from California, not MA). Rock and sediment in the ice make the glacier base 'a kind of coarse sandpaper that is capable of scratching bedrock'. This leaves 'striations or striae, on the rock surfaces that can reveal the direction that the glacier was flowing'. Also describes 'glacier polish'.
  • pubs.usgs.govUSGS Bulletin 839, Laforge, Geology of the Boston Area, Massachusetts, 1932 (primary, federal). 'The Wisconsin ice sheet approached from the northwest and moved over the area in a southeasterly direction. Glacial striations and small grooves are abundant on the ledges' ... 'general direction of movement was about S. 15° E.' Also: 'Striations with a more easterly trend are preserved on many ledges'. WebFetch returned 403, so this was read through a direct download (curl) plus pdftotext in this session.
  • sites.tufts.eduTufts University, J.C. Ridge, The Surficial Geology of the Middlesex Fells Reservation, version Dec. 5, 2019 (university, primary mapping). 'Ice striations are abundant!' 'Overall, striations trend to the south-southeast'. Older 'striations with a southeast to east-southeast direction' survive on hilltops. The area was deglaciated 'about 17,000 years ago' (stated as the author's working hypothesis).
  • bpb-us-e1.wpmucdn.comTufts self-guided tour of the Skyline Trail, Middlesex Fells, Part 5 (Jack Ridge). Shows the features are visible to a walker on a public trail: 'At the top of the hill, look for the glacial grooves left by glacial ice sliding across the top of the hill'. 'The grooves are oriented S24°E.' Another smooth outcrop: 'glacial striations are not well preserved here.' Safety: 'In wet or winter weather, some rock surfaces are very slippery' and stay on marked trails, 'a way of avoiding poison ivy and ticks'. (This is the redirect target of sites.tufts.edu/fellsgeology/files/2025/06/Skyline5-GrindingRockMollySpring-SelfGuide.pdf.)
  • pubs.usgs.govUSGS Open-File Report 81-651, Koteff and Stone, Friends of the Pleistocene guidebook, Nashua River Valley, 1981 (primary, central MA). At one stop, striations 'trend S36°W to S41°W, about 45° west of the regional south-southeasterly trend of upland striae and drumlins.' This supports SSE as the regional central-MA direction and shows local exceptions. Read through a direct download in this session.
  • pubs.usgs.govUSGS Bulletin 1163-C, Eschman, Surficial Geology of the Athol Quadrangle, Worcester and Franklin Counties, 1966 (primary). Glacial erosion 'is shown directly by striae, grooves, and smoothed and polished surfaces on bedrock ledges'. But 'No striations or grooves on bedrock were found within the quadrangle', because of coarse rock, and in schist 'any striae produced have since been destroyed by weathering.' This supports the not-every-ledge step. Read through a direct download in this session.

Checked against these sources on November 10, 2026.

In the guide for April, May, June, July, August, September, October, November

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