McKownville Improvement Association
Geology and geological history of McKownville NY

Geology summary
diagram of
      geological strata below McKownville
The ground in McKownville, at the surface, consists of a fine sand in most of the area, termed the Colonie Sand by geologists. It extends over a larger area of the New York Capital district, and is the essential foundation of the vegetated sand dunes and sand plain of the Albany Pine Bush. Bore holes show that this sand layer is up to about 70 ft thick just north of McKownville, with dunes up to about 50 ft high on top of this sand blanket. The sand was deposited as the underwater part of a large delta originating from the precursor of the Mohawk River where it entered the glacial Lake Albany near the present village of Scotia. As the lake drained and the water level lowered in stages, to around 13,000 years ago, the exposed sand was blown by the strong peri-glacial winds of that time into the dunes now seen in the Pine Bush area. One of these dunes forms the hill north of Waverly Place (or more exactly what is left of it after the University construction in the 1960's cut away the northern part). The Colonie Sand is the container (the unconfined aquifer) of the shallow groundwater in McKownville.

At an elevation of about 190 ft above sea level in McKownville, seen in the valley of the Krum Kill stream, and in a few boreholes that were sufficiently deep, the sand lies on a geological layer consisting of clay with many very thin silt laminations in it, called the Albany Clay. Geologists term this kind of material "varved clay", and it is a distinctive deposit of glacial lakes. Streams flowing into the lake bring seasonal summer melt water from the nearby glacier, which mixes with and suspends silt and clay particles into the lake waters, from which the coarser silt settles out to the lake floor in summer, and the finer clay settles out later in winter, after meltwater input ceases. Each layer of silt to clay in these deposits represents one year's deposit, and they can be counted up, in a borehole core for example, to estimate how long the lake existed (several thousand years for this lake, which is called Lake Albany). A borehole record obtained near Indian Pond on the University campus (diagram to the left) show that the Albany Clay is about 95 ft thick in this area.

Below the Albany Clay, only seen in a few boreholes near McKownville, there are materials deposited at or near the glacial ice front as it retreated north through this area about 15,000 years ago. These consist mainly of the deposits that geologists term glacial till (clay without layering, and containing rock fragments, material eroded and transported by the glacier). This was deposited at the base, or at the terminus of the glacial ice, but there can be local gravel and sand (from meltwater transport) instead of, or as well as, the till. These deposits vary a lot in thickness from one place to another; in some places there may be just a foot or so, in others more than a hundred feet.

These glacial deposits rest on bedrock, which below McKownville, and in the Capital District generally, consist of shales, and in places sandstones in shale, much older than any of the glacial and post-glacial deposits. Fossils found in the shales are characteristic of the later Ordovician geological time period, and the deposition of these strata and the fossils preserved in them are now known, from isotopic dating of suitable rocks elsewhere, to have occurred about 455 million years ago, in a time interval of several million years duration. These bedrock strata are not exposed at the surface in McKownville but can be seen easily not far away in the area, for example at Cohoes Falls and the gorge of the present Mohawk River below the falls, most accessibly in Peebles Island State Park. These shales and sandstones are, in the eastern part of the Capital District, not in horizontal strata as they were deposited; they were tilted, folded and deformed by extensive faulting, mainly about 450 million years ago in the first of the several events of mountain building that created the Appalachian deformed belt of eastern North America from this time up to about 300 million years ago.

The regional context of the young part of this local geological history:

The retreat of the Laurentian continental ice sheet
Map of the positions of the front of the Laurentian ice sheet in eastern New York and New England starting from the maximum extent 23,000 years ago, when the ice front was at the position of Long Island, to crossing the NY-VT border with Quebec about 13,200 years ago. Numbers on the map are in 1000's of years before present (present defined as 1950CE). As the ice retreated north, glacial lakes grew in the major valleys (see diagram below).
 Map and age data compiled on it is an image from and the product of the North American Glacial Varve Project, Tufts University.
map of Laurentian ice front positions 23 to 13 thousand years

The glacial lakes of New England and adjacent New York and Quebec
glacial lakes of
      New England
diagram simplified from a map of the New England Varve Chronology (NEVC) Project.
Maximum extents of the large glacial lakes of this region; the lakes reached the extents shown at different times, so this map is not a view of the geography of a single time.
Hachured line through Long Island is the former maximum extent of the Laurentian Ice Sheet (see map above).
Green and violet bars and red boxes are sections where varved clay layers have been counted, and correlated into an overall time sequence. See the Varve Project website for all the details.

photo of
      varved silt and clay layers showing annual alternation

photo of core sample of varved clay and silt showing the annual alternation from silts (lighter grey) to clay (darker grey). Yellow arrows point to the base of the silty layers. One year's deposition of silty material (summer - S in the coloured bar), and the clay layer (winter - W in the coloured bar).
Black and white bar scale on the left is divided in centimeters (2.54 cm to an inch).
 These varve layers are significantly thicker (particularly the silt portions) than is typical of varved clay deposits, being from a location close to the mouth of a former stream entering a glacial lake. This is chosen to provide a clear illustration of the seasonal variation and the layers.

Photo from the North American Glacial Varve Project website.

Proto-Great Lakes discharge through the Mohawk Valley into Lake Albany
map of
      Laurentian ice and marginal lakes about 14500 years ago
Map reconstruction of the Laurentian ice front and adjacent developing Great Lakes about 14,500 years ago. At this time, drainage from the early parts of the future Lakes Huron and Erie flowed east along the southern margin of the ice lobe occupying the area of future Lake Ontario and (indicated by the blue arrow) down the Mohawk Valley into Lake Albany (just off the edge of this map). This large discharge created the gravel and sand delta of the Mohawk in Lake Albany, the origin of the Colonie Sand.

Lake Albany shorelines
Lake Albany at the time it was most extensive had shorelines in the Capital District near present-day elevation of 310 ft above sea level, and all of the area now McKownville was then 50 feet or more below the surface of the lake. The lake level fell in several distinct stages, as the moraine dam at the south end near New York City began to be overtopped and cut through. One particularly prominent stage (termed Lake Quaker Springs) has shoreline features near 250 ft above sea level in this area, of which remnants exist in the area west of Fuller Road near the McKownville-City of Albany boundary. Lower temporary shoreline features of Lake Albany at several levels down to one at 192 ft elevation can also be found in McKownville; one with a base elevation of about 216 ft forms the south-facing slopes crossing the middle parts of Glenwood and Norwood Streets. In McKownville, the local remnants of these lake shorelines that were cut into the Colonie Sand alternate with very gently sloping terraces which are the product of smoothing of the shallow near-shore lake bottom, by waves and perhaps also lake ice activity, locally redistributing the sand. Small stream channels formed after the lake levels fell below each shoreline-terrace pair dissect these landforms in places, and the larger stream channels of the two branches of the Krum Kill cut locally through all of the terraces and shorelines below 250 ft elevation. This topographic and geological profile section, drawn on a line running parallel to and between Parkwood and Glenwood Streets in McKownville (vertical  scale is enlarged from the natural proportion to make the surface topographic variations more obvious) shows two of these lake shore slopes and the terraces below:
      and geological section through north side of McKownville

Extinct fauna - mastodonts
After the glacial moraine dam near new York City failed and was cut completely through by the Hudson River, Lake Albany ceased to exist. The former lake bed became vegetated, and occupied by Native Americans and the fauna they hunted. Early in this history, and perhaps from before Lake Albany had fully emptied, large mammals now extinct were present, including the mastodont. One relatively complete skeleton of this animal was found in 1866 near Cohoes Falls, during preparations for construction of one of the Harmony Mills factory buildings; this is on display in the New York State Museum in Albany, as is an excellent diorama of a mother mastodont and her calf, in an appropriately cold, snowy upstate New York winter landscape:
New York State
      Museum mastodont diorama 

There is an online exhibition for the Cohoes Mastodon on the NYS Museum website.

Sand dunes of the Albany Pine Bush
During and after the drainage of Lake Albany, sands of the old Mohawk River delta were in part redistributed by winds, probably often strong and very cold, as experienced now in areas near large continental ice sheets, because of the large temperature gradients between the elevated glaciated area and the land nearby. Before vegetation developed and stablised the dunes, migration of sand must have been significant whenever the wind blew vigorously. Many of the dunes in the Pine Bush near McKownville have long straightish limbs running WNW-ESE, parallel with the prevailing direction of these strong winds, and end in hooked and curved downwind terminations, a form termed "parabolic" dunes. A map below shows the distribution of these in the area near McKownville, derived from the 1953 USGS topographic map. This map shows the topography before it was extensively altered by large construction projects, of the State University and State Office campuses, the major multilane highways, shopping malls, etc, which have destroyed many of the dunes since that map was surveyed and drawn. Prominent dune forms shown by orange areas; yellow are local extensions to some dunes drawn from more recent and detailed topographic information. These are just the topographically prominent features; the wind-transported sand also blankets a large proportion of the area between the dunes.
sand dunes
      near McKownville map
The Albany Pine Bush Preserve contains extensive walking trails in areas where the dunes, and the pine barren vegetation are intact, to the west of the area shown in the map above. For walking where dunes are prominent, these trails are recommended:
the northern part of Karner Barrens, Blueberry Hill West, the western part of Truax Trail Barrens, Kings Highway Barrens, and Great Dune.

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