Rockin' around Rockport Harbor

Introduction

Rockport village and its scenic waterfront are among the most popular tourist destinations on the Maine coast. The Maine Geological Survey has mapped the surficial geology of the Rockport area during the 2009 field season. This work, together with previous studies of the area's bedrock geology, has revealed sites of geologic interest in the vicinity of Rockport harbor. Several of these localities are publicly accessible thanks to a network of parks, trails, and conservation properties. The text and photos in this website will introduce you to places around the harbor where you can see highlights of the local bedrock, glacial, and economic geology.

Rockport waterfront parking area and Cramer Park

A good place to start is the town park at the head of the harbor (Figure 1). The remains of several old lime kilns can be seen next to the parking lot (Figure 2). These structures are remnants of the lime industry that flourished around Rockport and neighboring towns during the 1800's. Limestone was quarried at numerous locations and then burned in the kilns to produce lime (calcium oxide) used in making plaster. Exhibits next to the Rockport kilns explain the process and its importance to the local economy (Figure 3).

Figure 1

Figure 2

Figure 3

Much of the limestone that was burned here came from a nearby quarry on Wiley Road in Rockport, just northwest of Simonton Corners (Figure 4). The quarry is now part of the Simonton Corner Quarry Preserve owned by The Nature Conservancy. Waste rock from the burning operation was disposed in heaps on the waterfront and along the banks of Goose River. You can visit Cramer Park (uphill and across the road from the harbor parking area), and walk along the tops of these large white piles next to the river (Figure 5). Much additional information on the history of the Maine lime industry is available in a book by Grindle (1971).

Figure 4

Figure 5

Figure 6

Visitors to the harbor park will also want to see the marble statue of one of Rockport's most famous "seasonal residents" - Andre the Seal (Figure 6)!

East side of Rockport harbor - Beauchamp Point Road

A series of well-exposed bedrock ledges (outcrops) can be accessed from Beauchamp Point Road. This gravel road follows the shoreline on the east side of the harbor. It may be closed to vehicles during the winter, but there is limited parking where the pavement ends, and foot traffic is welcome. The roadside ledges described here do not require permission to visit, but the shoreline is private farther south where the road curves away from the harbor.

As you follow the road south, two very short paths will bring you down to shoreline outcrops with nice views of the harbor and Indian Island lighthouse in the distance. Figure 7 and Figure 8 show the first outcrop, which has been sculpted and grooved by overriding glacial ice. This abrasion resulted from the grinding action of rock debris carried in the bottom part of the most recent continental ice sheet that covered New England. Similar abraded rock surfaces are exposed in many places along the Maine coast, where the sediment cover has been eroded away by rising sea level. The glacial grooves seen here indicate ice flow in a generally south-southeast direction.

Figure 7

Figure 8

A short distance farther down the road, there is a broad ledge on a point where the shoreline is indented (Figure 9). The eastern side of the point has a rock surface showing sets of glacial grooves trending in two directions. The dominant set trends 163º (SSE), and is indicated by the red pencil in Figure 10. The pencil points in the direction of ice flow. The blue pen is parallel to the other set, which trends 137º (SE). The latter grooves are inferred to be older, because they are in a small shallow depression on the ledge surface and thus protected from the later onslaught of the ice flow that engraved the 163º set.

Figure 9

Figure 10

Continuing along the road, you will notice one of several outcrops of prominently layered rock on the east side of the street (Figure 11 and Figure 12). This is the Coombs Limestone - the same rock formation which was quarried in Rockport and burned in the waterfront lime kilns. Unlike many of the metamorphosed and scrambled rock formations in southern Maine, this one clearly shows the original sedimentary stratification from having been deposited on an ancient sea floor. Here the strata have been dramatically folded by stresses in the Earth's crust. The close-up view (Figure 12) shows how weathering of the outcrop surface has revealed thin ribs of resistant material parallel to the axis of the fold (parallel to blue pen in photo). These are layers of harder, silica-rich mineralization that formed along cracks in the rock produced by deformation of the limestone (Osberg et al., 1995).

Figure 11

Figure 12

These and other bedrock exposures along the shore of Rockport harbor have been studied by geologists for many years (e. g. Hitchcock, 1862; Osberg et al., 1995). A geologic map and summary of recent work in the Camden-Rockport area is provided by Berry and Osberg (2000). The Coombs Limestone is tentatively thought to be of Precambrian age. It is part of a stack of rock formations called the Rockport Sequence. This and other rock sequences in the area are bounded by faults, and their relation to the broader history of shifting plates of the Earth's crust (terranes) has yet to be fully understood.

References

Berry, H. N., IV, and Osberg, P. H., 2000, The Megunticook Formation, in Yates, M. G., Lux, D. R., and Kelley, J. T. (editors), Guidebook for field trips in coastal and east-central Maine: New England Intercollegiate Geological Conference, 92nd annual meeting, October 6-8, 2000, Orono, Maine, p. 54-70.

Grindle, R. L., 1971, Quarry and kiln: the story of Maine's lime industry: The Courier-Gazette, Inc., Rockland, Maine, 331 p.

Hitchcock, C. H., 1862, Geology of Maine [includes contributions by G. L. Goodale, O. White, and E. Holmes]: Maine Board of Agriculture, 7th Annual Report, p. 223-430.

Osberg, P. H., Tucker, R. D., and Berry, H. N., IV, 1995, Is the Acadian suture lost?, in Hussey, A. M., II, and Johnston, R. A. (editors), Guidebook to field trips in southern Maine and adjacent New Hampshire: New England Intercollegiate Geological Conference, 85th Annual Meeting, October 6-8, 1995, Brunswick, Maine, p. 145-171.

Thompson, W. B., in prep., Surficial geology of the Camden quadrangle, Maine: Maine Geological Survey, open-file map.

Text by W. B. Thompson with contributions from H. N. Berry IV.
Photos taken by W. B. Thompson, 2009.

Originally published on the web as the December 2009 Site of the Month.

Last updated on January 7, 2010