Cretaceous Exposures
Glacial tectonics is responsible for these exposures. Myron Fuller's 1914 publication (U.S.G.S. Professional Paper 82) built on the earlier work of Veatch. Fuller describes overturned folds in which clay has behaved like a shale. These types of features are mainly seen out east.
Jaynes Hill, the highest point on Long Island, contains a stack of Cretaceous material. The same unit has been mined south of Jayne's Hill in back of the Hilton on Route 110.
In 1904, Arthur Hollick published a work on fossil plants of Long Island, including winged seeds. In Late Cretaceous, Long Island was dominated by a coastal forest on deltaic sediments. This included a conifer-dominated forest, a precursor of today's Pine Barrens.
Lignite may represent charred wood resulting from fire.
On Long Island, 90% of "Indian paint pot" concretions are Cretaceous. They form very quickly as iron oxide precipitates from groundwater. They often are filled with clay, but sometimes have pyrite, marcasite, lignite, melanterite, or hematite, instead. On occasion, the pyrite may contain some copper. Sometimes concretions are covered with little squares, which are hematite pseudomorphs after pyrite.
If a concretion forms in a zone that is alternately wet and dry, it may become a septarian. This occurs if it cracks, and the cracks fill in with mineral material such as goethite.
Sometimes, nails or other metal can be found, around which a concretion is forming.
In the Cretaceous, sandstone facies are limited, but they must occur somewhere.
Fulgurites, which are rare on Long Island, are created by lightning strikes.
Native Americans used Cretaceous clay for pots. After firing, the clay was brick-red.
In colonial times, Europeans made bricks, pottery, and jars. One example of a Long Island-based brick company that is now out of business was the Nassau Brick Company.
Long Island's glacial sediments are like a blanket draped over the underlying Cretaceous sediments. Eleveated areas occur over Creaceous highs.
The spreading of the Atlantic subsequent to the breakup of Pangaea made the East Coast of North America into a coastal plain. The East Coast became a passive continental margin. The West Coast was the leading edge of North America, and that is where mountains formed.
Glaciation occurred in Africa during the Cretaceous. Streams became rejuventated in North America, and deltas formed on the coast. During much of the Tertiary, marine waters covered large parts of the southeastern United States.
By late in the Cenozoic, North America had migrated far enough to the north for seasonal effects on the weather to become pronounced in the northern part of the continent.
Glaciers are gravity-driven. The mineral, ice, accumulates and flows. Pressure can melt the bottoms of glaciers and enable them to glide.
Louis Agassiz grew up in Switzerland observing mountain glaciers, also known as valley glaciers. In addition to these types, continental glaciers also exist, and this is is what created what is now Long Island's surface during the Pleistocene.
Agassiz noticed rocks at the edge of the glacier as well as other rocks way down the valley past the glacier. He called the rocks moved by the glacier "erratics" because they were different from the local bedrock, and could be considered "stones out of place". He applied the principal of "uniformitarianism to his findings. Uniformitarianism states that "the present is the key to the past". His conclusion was that in the past, sheets of ice had covered almost all of Europe. At first, this idea was met with great skepticism. However, the evidence ultimately convinced other geologists that Agassiz was correct.
He eventually became a professor at Harvard. He found evidence that glaciers had covered the northern half of North America.
The former locations of edges of glaciers are marked by moraines. These occur typically in the form of hills.
Till is ice contact sediment that is poorly stratified or not stratified at all and contains a mixture of boulders, gravel, sand, silt, and clay, generally unsorted. Gumbo till is deeply weathered and contains boulders that can be crushed by hand.
Surprising to many, most of the Pleistocene has had a climate similar to that of today. The Plesitocene is better described as a time of dramatic climate change than a time of glaciers. The moderate climate was punctuated by short cold periods.
What influences climate?
Lots of snow is needed to make continental glaciers. The ice sheet that last visited North America may have locked up enough water to lower the oceans by 400 feet. An ocean current like the Gulf Stream could bring moisture to the Arctic in large quantities, resulting in the requisite amount of snow.
At the southern edge of the glacier, the climate melted the ice as fast as it could accumulate through precipitation and advance. Moraines formed here.
Types of Moraine
Three Ways in Which a Glacier Affects Bedrock
Much of the material that makes up central and eastern Long Island may have come form the Connecticut Valley.
The Pleistocene (Oldest at Bottom)
| Europe | North America | ||
| Glacial | Interglacial | Glacial | Interglacial |
| Wurm | Wisconsinan | ||
| Riss-Wurm | Sangamon | ||
| Riss | Illinoian | ||
| Mindel-Riss | Yarmouthian | ||
| Mindel | Kansian | ||
| Gunz-Mindel | Aftonian | ||
| Gunz | Nebraskian | ||
Last modified September 29, 1997