CU Maurice River members listen attentively to Mark Demitroff as he describes periglacial features on the Maurice River Bluffs preserve. Photo: Joan Lawrence-Rhoads
On March 15, I was fortunate to participate in a CU Maurice River walk led by Mark Demitroff on The Nature Conservancy’s (TNC’s)Bluff Preserve in Millville. Located just south of center-city Millville on the west bank of the Maurice River, this site is one of TNC’s most visited parcels. Possibly you’ve been there, but it is my hope that by sharing some of Mark’s esoteric facts you might consider the concepts when you return—or visit for the first time.
Answering the question “Who is Mark Demitroff?” can lead to a complicated response. He has lived a life of intellect with a grand diversity of interests, many of which are centered, as an old-fashioned geographer, on the Pinelands. His pursuits lie at the intersection of cultural, environmental, and natural histories. An adjunct professor in the Geology Department at Stockton University, Demitroff twice served on the board of the U.S. Permafrost Association, and sits as a board member of Stockton’s South Jersey Culture & History Center.
Demitroff’s expertise is periglacial geomorphology—the study of non-glacial processes in cold areas past and present. He focuses on ice age environments, when deep seasonal frost and past permafrost profoundly affected South Jersey’s land surface. He has authored and co-authored numerous journal publications on cold-climate, frost cracks, permafrost thaw, wind-etched stones, and ancient dune fields, mostly borne of the cold, dry, and windy conditions during the Late Pleistocene era, particularly in the New Jersey Pine Barrens.
Mark’s book, Soggy Ground: A Geography of Pine Barrens Wetlands, discusses how to interpret the wetlands of the Pine Barrens through land-surface processes. The book’s promotional description reads, “Little-known ice age landforms provide critical habitat for plants and animals. Places like spungs, cripples, blue holes, and savannahs are woven together in a geographic tapestry of interactions between nature and society. People here have exploited these wetlands for millennia, features that now slowly fade from memory and place.”
Our walk began by looking at ventifacts—desert gravels that have been shaped by wind-driven sand or dust-laden ice crystals. These geologic time-travelers have surface features that can be analyzed for clues into the distant past. Mark showed us small stones that would have been polished and etched by strong winds across frozen ground—the polar desert-like landscape that prevailed when the continental ice sheet came closest to southern New Jersey. He explained how the surface of a single grain of sand can be analyzed to disclose the frigid temperatures that it was exposed to in the past, the timing of grain wind transportation, and when that grain thawed as permafrost waned. All of these are data used to build climate models. Working with colleagues nationally and worldwide, he unlocked the paleoenvironmental secrets held by deceptively complex Cumberland County quartz grains. Currently, Mark is collaborating with Canadian, Polish, and U.S. research institutions on ice age dunes systems, ancient river channels, past permafrost in the Appalachian Mountains, and prehistoric frost cracks preserved in the Devonian rock record.
The Nature Conservancy provides excellent mapping and marking of the bluff trails. Source: TNC website also posted at parking lot kiosk.
White dots show the course of the CU Walk as described in this article.
To make inferences and proper assumptions about a past landscape by looking at what is present currently, one must know the full history of a location. In the case of the Maurice River Bluffs, knowing that sand mining took place on the site is important to knowing the former topography dating back more than 12 million years ago. Mark sees beyond the present disturbed state of a site to formulate how it was formed and to understand its past nature.
Early miners first sought sugar-sand silica for glassworks from the banks of the Maurice River. Well-sorted clean loose grains of windblown sand would have been deposited in a blanket that filled old valleys and depressions carved into the bank. Excavations were labor intensive, being hand-dug. Mining at the time was selective and conducted in a more surgical fashion than present day machine-based operations, hence the patchwork nature of the Bluff’s diggings. In the mid-1800s workers’ tools were shovels, pick-axes, and animal-drawn wagons—not large diesel-fueled excavators.
Today’s LiDAR (short for “light detection and ranging”) mapping tools allow scientists like Mark to view the remaining carved landscape of hills and valleys that apparently trapped windswept sands. There is much to learn. The Bluff’s resultant topography offers further proof of Mark’s long-held belief that our local landscape was frequently frozen and thawed while being scoured by cold, dry katabatic winds (a wind that blows down a slope or hill due to gravity) that flowed off a nearby continental ice sheet. LiDAR is a laser technology that maps the Earth’s topographical surface from above, using airplanes, drones, and satellites. You may be familiar with it being used to discover the vast empire of the Mayans, where the degree of clarity allows the trained eye to see the outlines of ancient cities and village foundations in Central America.
Sand was loaded and barged at wharfs on what is now The Nature Conservancy Maurice River Bluffs Preserve. Photo: Joann and Dale Wettstein, Steelman Photo
Pettinos Sand Co. circa 1900 mined the Maurice River Bluffs preserve via wagon. Photo: Joann and Dale Wettstein, Steelman Photo
Armed with these images and a plethora of additional scientific evidence, geomorphologists like Mark can determine that although the Laurentide Ice Sheet (starting 2.5 million years ago) stopped north of our region about 51 times—with the last advance halting near present day Exit 11 on the New Jersey Turnpike—our region is indeed shaped by a glacial past. Periglacial processes are potent—albeit poorly understood—geomorphic agents that ravaged our landscape. The Laurentide Ice Sheet at its maximum was 30 percent larger than its present-day counterpart in Antarctica. In its full extent it was one or two miles thick. At the glacial maximum, sea level here was 433 feet lower than it is today.
We visited the old stone Ferguson Farm house and our geologist guide asked us where the large stones came from. My first guess was Pennsylvania, but Mark explained that some stones used in local construction were actually ballast stones from European ships. In fact, ports in Philadelphia often acquired cobblestones for streets when ballast stones were off-loaded and replaced with cargo. We phoned octogenarian Richard Weatherby, whose grandfather owned the house after Ferguson. Richard said he was told that they were indeed New York State ballast stones, offloaded and exchanged for sand on the return trip. These were valued commodities at either end of a trade deal. As early as the 1790s, Maurice River glass sand was barged to the Pitkin Glass Works near Hartford, Connecticut. Just fascinating, I think you’ll agree!
Next week we will continue our story about New Jersey’s cold, dry, and windy conditions during the Late Pleistocene era starting with tools used to ascertain the past. Maps made by Charles Hartman and present day LiDAR mapping will be part of that discussion.
Find out about CU Maurice River’s outdoor opportunities. Visit CUMauriceRiver.org and select the calendar from the home page.
Sources
Demitroff, Mark, Soggy Ground: A Geography of Pine Barrens Wetlands, South Jersey Culture & History Center,February 9, 2024
Coal Was an Early Product of the Pine Barrens, By J.G. Wilson, Batsto Citizens Gazette, 1987. www.co.ocean.nj.us
