Haskell Rock, East Branch Penobscot River, T5 R8 WELS

Photo by Bill Forbes

Location

The East Branch of the Penobscot River flows southward from Grand Lake Matagamon, just to the east of Baxter State Park (see regional map). The East Branch has been a popular river for recreational canoe trips since Maine's first ecotourist, H. D. Thoreau, described his guided excursion down the East Branch in "The Maine Woods" (1864).

The first six miles downstream from the Grand Lake Road are more or less smooth paddling (except for Stair Falls), as far as the Haskell Deadwater. This is followed by a three-mile stretch of whitewater rapids and falls including Haskell Rock Pitch, Pond Pitch, Grand Pitch, Hulling Machine Falls, and Bowlin Falls. The first of these, Haskell Rock Pitch includes Haskell Rock itself, a distinctive 20-foot high pillar in the middle of the river. According to E. S. C. Smith 1928), "the rapids or 'pitch,' take their name from that of an unfortunate lumberman who lost his life at this spot many years ago." (But see note about historical map error.)

The Haskell Rock Conglomerate

Cobble in conglomerate

Haskell Rock is made of conglomerate, a distinctive sedimentary rock composed of pebbles or larger stones that were embedded in mud or sand and hardened into rock. Conglomerate forms in places of rapid erosion and deposition, such as near shorelines or in fast-moving streams, where stones of various sizes are deposited together. For the Haskell Rock conglomerate in particular, the stones have a range of shapes, sizes, and compositions, though rounded pebbles and cobbles are common.

The conglomerate can be traced in outcrops for some distance to the northeast and southwest of the river Rankin, 1961), which indicates that the pillar in the stream is an erosional remnant of a more extensive bedrock unit. Many boulders of the conglomerate, broken from the underlying bedrock by the force of glacier ice or river flow, are scattered about the river in this vicinity. But Haskell Rock itself is a protrusion of solid rock, and remains attached to the underlying bedrock. Erosion has begun to eat into the sides of the rock, and will continue to wear away the pedestal until eventually the rock topples into the river.

Conglomerate
boulders

Haskell Rock

Erosion

Geologic Significance

In addition to being fascinating to look at, conglomerates attract special interest from geologists because they generally reflect a dynamic time in geologic history, commonly marking a change from one geologic environment to another. This is the case for the Haskell Rock conglomerate. Because the rocks in this area have been tilted (Rankin, 1961), older layers are exposed to the southeast and younger layers (view upstream) are exposed to the northwest. From the geologic map then, we can see that the conglomerate is between a succession of unnamed Ordovician volcanic rocks below, and marine sedimentary rocks of the Devonian Seboomook Formation above. (Click to see the Geologic time scale for the Paleozoic Era.) During the transition from active volcanic islands to an ocean basin with deeper-water sedimentation, a variety of rocks from the older islands were eroded to produce the conglomerate. Thus the Haskell Rock conglomerate contains stones of volcanic rock, slate, sandstone, black chert, quartz diorite, and milky quartz (Smith, 1928; Rankin, 1961) which were eroded from the older units.

Rocks upstream

Geologic map

Similar units of conglomerate are found resting on Ordovician volcanic rocks elsewhere in northern Maine, which are interpreted as the eroded remnants of Ordovician volcanic islands (Neuman, 1984). In many places, the conglomerates and related near-shore sediments in northern Maine were deposited in Early Silurian time. The section at Haskell Rock, however, is somewhat older, dated as Late Ordovician (Ashgill) age (Neuman and Rankin, 1980; Neuman, 1980). The section from Pond Pitch to Haskell Rock is the thickest and apparently most continuous exposure of rocks this age in Maine (Neuman, 1980).

Geologists Attracted to this Spot

The most recent careful work was done in 1976 by Dr. Robert Neuman assisted by Dane Sparrow, who described a measured stratigraphic section along this part of the river, and reported on its paleontology (Neuman, 1980). Doug Rankin described the Haskell Rock conglomerate and mapped its relationship to surrounding rocks as part of his Ph.D. work in this area (Rankin, 1961). Edward Smith (1928), of Union College, spent "a short time" in the summer of 1927 studying the conglomerate at Haskell Rock and suggested that it might be a glacial deposit (an idea subsequently disproved by Rankin, 1961). Dr. John M. Clarke (1909) mentions "a coarse conglomerate" at Haskell Rock, though being a paleontologist he was disappointed at finding no fossils in it. Even the earliest geologic explorations of Maine made note of this distinctive rock, undoubtedly due to its prominence and easy access. Charles H. Hitchcock (1861) mentions "a very coarse conglomerate" in T5 R8. Ezekiel Holmes (1839) lists "puddingstone", an earlier term for conglomerate, among the rocks of this area. This history is typical of many places in Maine where the early geologists made note of interesting occurrences in their reconnaissance surveys, but left it to later workers - even a century later - to take the time to draw out the details.

Geologists

The Geological Society of Maine included Haskell Rock as part of its annual summer field trip on July 23, 2005. We are grateful to participants on that trip who provided photographs for this web site.

References Cited

Clarke, John M., 1909, Early Devonic History of New York and Eastern North America: New York State Museum, Memoir 9, Part II, 250 pp. (Note: This publication is for sale from the New York State Museum under the title: Annual Report of the New York State Museum, No. 62, v. 4. Check the NYSM current publication list for price and ordering information.)

Hitchcock, Charles H., 1861, General report upon the geology of Maine: in Preliminary report on natural history and geology: Maine Board of Agriculture, 6th Annual Report, p. 146-328.

Holmes, Ezekiel, 1839, Report of an exploration and survey of the Territory on the Aroostook River during the spring and autumn of 1838: Maine, Board of Internal Improvements, Augusta, Maine, 78 p.

Neuman, Robert B., 1980, Trip B-4: The core of the Weeksboro-Lunksoos Lake anticline, and the Ordovician, Silurian, and Devonian rocks on its northwest flank: in Roy, David C., and Naylor, Richard S. (editors), A guidebook to the geology of northeastern Maine and neighboring New Brunswick: New England Intercollegiate Geological Conference, 72nd Annual Meeting, Presque Isle, Maine, p. 114-126.

Neuman, Robert B., 1984, Geology and paleobiology of islands in the Ordovician Iapetus Ocean; review and implications: Geological Society of America Bulletin, v. 95, no. 10, p. 1188-1201.

Neuman, Robert B., and Rankin, Douglas W., 1980, Bedrock geology of the Shin Pond-Traveler Mountain region: in Roy, David C., and Naylor, Richard S. (editors), A guidebook to the geology of northeastern Maine and neighboring New Brunswick: New England Intercollegiate Geological Conference, 72nd Annual Meeting, Presque Isle, Maine, p. 86-97.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine: Maine Geological Survey, scale 1:500,000. (Note: This map is for sale from the Maine Geological Survey under Publication Code BGMM for $5.00 plus tax. Contact us to order by phone, or use our publication search page to generate an order form that can be sent by fax or mail.)

Rankin, Douglas Whiting, 1961, Bedrock geology of the Traveler-Katahdin area, Maine. Unpublished Ph.D. thesis, Harvard University, Cambridge, Mass., 317 p., 4 plates.

Smith, Edward S.C., 1928, A possible tillite from northern Maine: American Journal of Science, Fifth Series, vol. XV, no. 85 - January, p. 61-65.

Text and captions by Henry N. Berry IV.
Photographs by Bill Forbes and Bob Johnston, July 2005.
Air photograph by U.S. Geological Survey, provided by Maine Office of GIS.
Topographic maps by U.S. Geological Survey.
Geologic map by Maine Geological Survey.
Graphic illustrations by Susan Tolman, Henry Berry.

Originally published on the web as the October 2005 Site of the Month.

Last updated on April 19, 2012