Colourful bluffs in Long Island recall the most recent ice age

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Deborah Painter (USA)

Imagine a tremendous piece of land moving equipment that scraped up the soil and some of the surface bedrock from four states within the United States’ Eastern Seaboard, carrying and dragging it all the way, before dumping it on a ridge off the shoreline. That is what essentially occurred with the final advance of the Wisconsinian ice sheet, the only one which left glacial deposits visible in New York State today. Long Island is a ridge of Cretaceous bedrock with glacial deposition. The moraines there have not been ground into sandbars and spits along the western end of the north shore as much as elsewhere, because of the sheltered nature of the Long Island Sound. Therefore, shoreline bluffs expose rocks as well as glacial loess.

Fig. 1. Fishermen’s Drive takes you to the loess deposits. To park at the beach requires a permit. (Photo by JB Steadman.)

If you find that your journeys take you to New York City, one of the world’s largest metropolitan areas, try to make time to visit Caumsett State Park at Long Island Sound. My own visit began when planning a visit to New York State’s Long Island to see my friend, Joyce Raber. She suggested various things that we might do: go to a Broadway play, go shopping and so forth. However, my list of things to do was typically “eco-tourist”. I wanted to visit the famed American Museum of Natural History in Manhattan, then see nearby Central Park, where the European starling was first released in North America (a bad decision made by a fan of Shakespeare’s works).

Another favoured destination was Caumsett State Park and the glacial tills. Joyce had mentioned it to me in the past and whetted my appetite. We followed the sign for the park when we arrived in the Huntington area and, after parking in the car park near the information booth at the park, learned from a ranger that we could take our choice of two roads to the beach — Fishermen’s Drive, two miles from the tidal flats and open beach (for which a parking permit is needed); or the Service Drive, which takes one past the Caumsett Outdoor Education Center, formerly a summer cottage on the old manor home of Marshall Field III, the department store mogul, whose home was donated to the state of New York to create this large park.

Fig. 2. Caumsett State Park’s bluffs overlook Long Island Sound. The Sound’s shelter from strong waves preserved the Pleistocene deposits. (Photo by JB Steadman.)

This section of the bluffs has more lacustrine (lake) deposits and the area accessed from Fishermen’s Drive has more yellow loess. We saw both and encountered a change in the topography as we approached the manor. (In fact, we took the Service Drive, collected rocks at the bluffs at the end of this Drive and then walked a little more than one kilometre west of the parking area to the bluffs that consisted partially of loess.) Marshall Field’s old English style home rests on top of the Sands Point Recessional moraine.

The bluffs average 90m above the mean sea level. Twenty thousand years ago, the beachfront here was a glacial lake. As the glacier advanced toward this location, it pushed forward the underlying Cretaceous and Pleistocene sediments. Faulting occurred and then the glacier advanced over the sediments, depositing till. The glacier then stopped. Loess (windblown silt and fine sand from the moraine), was deposited here because of the difference in air pressure. One sees this in valley glacier ice fronts as well. In these areas, the cold air of the glacier meets the warmer air of the sea. Loess is uniquely yellow and the deposits here can be as much as a metre in thickness.

Fig. 3. Severely weathered and eroded metamorphic red slate is common at the beachfront, where it came to rest after being dragged across hundreds of kilometres. (Photo by David W Cunningham.)

Colourful rocks were all around us on the beach. Metamorphic and igneous rocks are predominant, since they could withstand the double punishment (of being scraped by other rock material and subject to mechanical weathering from freezing and thawing when partial melting occurs) not endured by the sedimentary rocks carried along. The metamorphic rocks at the sea cliff are red slates, schists (easily recognised because of their distinctive foliation), metaconglomerates, gneisses and quartzites. Among the igneous rocks we found were basalts, granites and andesites, of the diorite-andesite family. Potassium, feldspar, quartz, biotite, plagioclase and amphibole are present in this rock named for the Andes Mountains and it is diagnostic of old subduction zones.

Fig. 4. Metamorphic schist sparkles with mica flakes. (Photo by David W Cunningham.)

Although specimens have visible crystals, they are volcanic. The ones at Caumsett have white ‘phenocrysts’ of plagioclase in fine black amphibole. Now, you may be thinking, “I remember my science teacher teaching us that fast cooling rocks have small crystals and slow cooling ones have large crystals. How can a single piece of volcanic rock have both large and small ones?” My former boss. Fred Davis, is a geologist and remains a friend. Fred told me that a volcanic rock can undergo two step cooling. First, lava is buried in a magma chamber of a volcano. The exterior forms crystals, while the matrix, meanwhile is still molten. Then, the partially crystallised magma is hurled to the surface and the matrix cools quickly to form the fine-grained crystals of black amphibole.

Fig. 5. Igneous andesite is among a number of igneous rocks brought to Caumsett State Park during the Pleistocene epoch. (Photo by David W Cunningham.)

Standing on the beach looking at the bluffs, Joyce and I enjoyed a moment of being transported back in time in our imagination to a time thousands of years ago, when the continental glacier ceased its march to the sea and began to melt. In our mind’s eyes, we stood on top of an immense ice mass at the ice front here at Caumsett, where cool winds blew yellow silt into our eyes. We also allowed ourselves to “hear” the flow of melt water into the Sound.

The park is a good location to take children and older adults to see an old terminal moraine and associated till and loess, because it is in a suburban area and there are no dangerous cliffs. Collecting rocks from the moraine is permitted only where the rocks have fallen from the bluff. Park officials forbid all climbing on the bluffs. For more information, call (631) 423-1770. The vehicle use fee is US$6. From the Queens metropolitan area, east on Interstate 495, take the Long Island Expressway from Queens and there take Route 110 north to Huntington. The address is 25 Lloyd Harbor Road, Lloyd Harbor, New York 11743.

Fig. 6. Collected at Caumsett. Top, left: metamorphic metaconglomerate; top, centre: metamorphic red slate; top, left: metamorphic mica schist with glacial scratches. Bottom, left: metamorphic schist; bottom, centre: igneous andesite; bottom, right: more igneous andesite. (Photo by David W Cunningham.)

About the author

Deborah Painter is an environmental scientist in the United States for a large consulting firm with headquarters in Aberdeen, Scotland. Her specialties are in wetland delineation and permitting, National Environmental Policy Act documents and hazardous materials site assessments.

Further reading

Dreimanis, A. 1988. Tills: Their genetic terminology and classification: In: Goldthwait, R.P. and Matsch, C.L. (eds), Genetic Classification of Glaciogenic Deposits. A.A. Balkema, Rotterdam. , pp. 17-83.

Erickson, Jon. 1996. Glacial Geology: How Ice Shapes the Land. Facts On File, Inc. NYC, NY 248 pp.

Gilbert, G. K. 1885. The topographic features of lake shores, p. 69-123 in U. S. Geological Survey, Annual Report, 5th (1883-1884), 469 pp.

Sirkin, Les. 1995. Eastern Long Island Geology with field trips. .Book and Tackle Shop, Watch Hill, Rhode Island 02891, 220 pp.

Sirkin, Les, 1996. Western Long Island Geology with field trips. Book and Tackle Shop, Watch Hill, Rhode Island 02891 179 pp.

VanDiver, Bradford B. 1985. Roadside Geology of New York. Mountain Press Publishing Company, University of Michigan. 397 pp.

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