The igneous rocks at Greenbrook are part of the Palisades Sill – Wikipedia. The rocks are mostly diabase. Research on the origins of the intrusion(s) is ongoing.
Rocks at Greenbrook
Geology
Ward Pound Ridge Greenery
Some mixed greens that we enjoyed seeing. The last image is a granite moss covered glacial erratic.
Pelham Bay 1 of 3
Marc and I went to Pelham Bay Park : NYC Parks in March. I like to make landscape photographs of the rocks and water. The colors were blue sky, yellow grass, and gray rocks. I added assorted skies and coloring.
The shoreline in Pelham Bay Park is crystalline basement rock of the Hartland Formation and part of Cameron’s Line. The park also has a variety of glacial materials and features.
The park encompasses 2,764 acres of coastal lowland. The Hunter Island Marine Zoology and Geology Sanctuary is on the north side of the Orchard Beach bathing area, and includes the northeastern shoreline of Hunter Island, and all of Twin Islands, Two Trees Island, and Cat Briar Island.
The Hartland Formation consists of granitic and garnetiferous amphibolite gneiss with many quartz veins and Migmatite dikes. Migmatite is an igneous rock that forms when metamorphic rocks begin to melt under high temperature. Felsic minerals melt and are injected into the surrounding rock along joints and faults in the rock. As the igneous material cools, bands of feldspar and quartz crystals form along the edges of the intrusion. The center of the migmatite veins contain larger crystals of feldspar and quartz. Migmatite stands out in outcrops as light-colored bands in the darker amphibolite gneiss host rock. Some dikes cut across older dikes and quartz-filled veins; many are folded or are offset by faulting. Overlying the bedrock is glacial till and numerous erratics.
Source: Geology of the New York City Region.
Also see Pelham Bay Park history
Rockefeller SP
We did a short hike to the Glacial Erratic at Rockefeller State Park Preserve (ny.gov) in Pleasantville, New York in Westchester County in the afternoon of Sunday September 15th. The granite rock is tilted 90 degrees from how it was originally metamorphosed deep beneath the Earth’s surface. There are white veins of lower meting po9int quartz that separated out during metamorphosis. 600 million years old. This mass of free-standing gneiss, almost 20 feet high and 65 feet in circumference, is probably the largest ”glacial erratic” to be found anywhere in the county. The glacier that transported the glacial erratic to Rockefeller State Park Preserve was part of the Late Wisconsin glaciation, which occurred approximately 20,000 to 25,000 years ago.
The activates look interesting. Maybe I’ll get a chance to try one or two.
Swan Lake is a lovely lake to walk around.
Luray Caverns
On a rainy day we decided to revisit Luray Caverns (Official website). The last time was several decades ago.
Luray Caverns, previously Luray Cave, is a cave just west of Luray, Virginia, United States, which has drawn many visitors since its discovery in 1878. The cavern system is adorned with speleothems such as columns, mud flows, stalactites, stalagmites, flowstone, and mirrored pools. The caverns host the Great Stalacpipe Organ, a lithophone made from solenoid-fired strikers that tap stalactites of varied sizes to produce tones similar to those of xylophones, tuning forks, or bells.
A Smithsonian Institution report of July 13 and 14, 1880, concluded: “[I]t is safe to say that there is probably no other cave in the world more completely and profusely decorated with stalactite and stalagmite ornamentation than that of Luray.”
Luray Caverns is privately owned by the Graves family, who have lived in Luray for many years. Theodore Clay Northcott, great-grandfather to the owners, purchased the land on which the caverns is located in 1905. (From Wikipedia)
Stony Man 2 of 2
Quotes about the Geology:
Stony Man Mountain itself is composed of ancient basalt (greenstone) that was metamorphosed through heat and pressure. The greenstone lava flows, which are approximately 570 million years old, now form the sheer, jagged cliffs of Stony Man and other peaks within the park. These flows, stacked one atop the other, create a unique topography of sheer cliffs and flat benches, contributing to the distinctive landscapes of Shenandoah National Park
The Geological Formation Of Shenandoah
The geologic story of Shenandoah National Park began 1 billion years ago. Molten magma, miles beneath the earth’s surface, slowly solidified to become the “basement rock,” or core, of what we know today as the Blue Ridge Mountains. For the next 500 million years, erosion and the uplifting of the earth’s crust exposed the granitic basement rock. You can see the granite component of this rock in Old Rag Mountain and its surroundings.
Over millions of years, the uplift of the earth’s crust formed deep cracks in the granite, which led to volcanic activity. For centuries, molten basaltic lava burst forth and poured over the land, forming a smooth, flat plain called the “Catoctin Formation.” (The bedrock underlying Big Meadows was formed by at least 12 of these lava flows which, collectively, are approximately 1,800 feet thick.) The cooling and contraction of the lava produced a network of polygonal cracks, or columnar jointing.
When continental drift (the separation of the Americas from the continents of Europe and Africa) began, about 600 million years ago, it formed a broad, shallow depression from Alabama to Newfoundland. Then, for 300 million years, an ancient sea flooded the area that is now the Appalachian Mountains. Layers of water-borne sediments accumulated on the ocean floor, followed by limestone sediments composed of fossilized marine animals and shells. The weight and resultant heat caused by the sediments eventually compressed the two layers into metamorphic rock.
As a result of the eons-old shifting of the earth’s tectonic (or crustal) plates, North America and Africa collided. This re-elevated and fractured the sea floor, causing the older, underlying layer of metamorphic rock to tilt upward and slide over the younger layer creating a towering mountain range that we call the Appalachians. The process occurred so slowly that even if geologists had been present, they would not have known that it was occurring. The new Appalachians probably looked more like the present Himalayas than the rounded mountains we see today.
The powerful forces of wind, water and frost have worn away the Appalachians for nearly 250 million years. These forces continue to create and refine the spectacular scenery of Shenandoah National Park. Water runoff, as demonstrated by the “500-year” rainstorm of June 1995, has carved the mountains’ distinctive alternating pattern of ridges and valleys. As you explore the park, look for signs of its geologic history and for how wind, water, frost and ice continue to sculpt the land.
Reference: History of Shenandoah APA Citation: Formation of the Shenandoah Region. Retrieved from OhRanger.com
In-Depth Geological Studies: USGS: New Geologic Map of the Shenandoah National Park Region
Geologic mapping in the Shenandoah National Park region of Virginia was conducted from 1995 to 2008 as part of a cooperative investigation between the USGS, National Park Service, College of William and Mary, and George Washington University, through the National Cooperative Geologic Mapping Program’s Educational Mapping component.
Available Downloads: Map PDF (37.8 MB) and Pamphlet PDF (103 pages; 1.7 MB). 2009, scale 1:100,000. USGS: A Hiker’s Guide to the Geology of Old Rag Mountain
Crystal Cave
We did a touristy thing and visited Historic Crystal Cave | First Show Cave in Pennsylvania (crystalcavepa.com). The history page is intersting. The cave was discovered in 1871 and some of the rock formations are a half-million years old (Crystal Cave (Pennsylvania) – Wikipedia.)
Manawainui Gulch Piilani Highway
The Manawainui Gulch under the Piilani Highway was formed by Haleakala’s waters carving out a deep chasm into the earth. The Manawainui Gulch is often dry unless there’s heavy rainfall, but the views of the southern slopes of Haleakala alongside the massive chasm are stunning. This area is very windy and it’s dangerous to get too close to any of the cliff edges. As you can see, were now on the dry side of the Island.
Piilani Highway is a road with bad reputation. We found it fun to drive. The road is rough and unpaved at times. It’s a good idea to honk around blind corners. Hawaii Route 31 is 61 km (38 miles) long, running from Kipahulu to Ulupalakua. It’s a twisty, up and down roller coaster. The toughest section of the road is about 10km (6 miles) long, where the road sometimes narrows to a single lane in sharp bends. In some areas (such as at Lelekea Bay) it’s just a one-and-a-half lane bumpy road hugging the sea cliff around a blind curve. The hairpin bends are completely blind, but there is almost no traffic. Occasionally the road is closed to traffic due to landslides. Traffic is light.
Piʻilani (“ascent to heaven”) was born ca. 1577 and ruled as Mōʻī of the island of Maui in the later part of the 16th century. At the time Maui was an independent kingdom within the islands of Hawaii. He was the first Aliʻi to unite the island under a single line.
