Posts Tagged 'Geology'


“Ithaca is Gorges” is awfully good branding. I thought the gorges that sliced away through shales and sandstones at the northern and southern edges of Cornell were gorgeous.Fall Creek in the rain during the morning. Most of this one is seen from above, on the Cayuga Trail. Only disconcerting thing: all the anti-suicide netting on the bridges.
Cascadilla Gorge in the late afternoon, after the sun had come out. We descended to town from the hill citadel of the university, right alongside the tumbling water.


The National Museum of Copenhagen is filled with flint tools from the pre-metal millennia. This stuff makes for very sharp edges. The stone of Europe’s Stone Age, flint stones were also used to start fires and spark guns into the 19th century. The Baltic beaches were littered with nodules of this dark chert. It’s a finely-grained quartz, not, as I first thought, obsidian (which is volcanic glass). This fist-sized and rather knuckle-like piece was my Swedish souvenir, found on a beach in Malmo. Here’s the verso and recto of a piece I split on the Northumberland coast a few years ago when my dearheart said the original piece was too large to carry back on the plane.The white coating here is typical. According to this site, “The thick white crust, the cortex, is not made of chalk, but of fine-grained opaline silica.”








There’s your beautiful world, NW edition. Here’s Masha Gessen, an old hand at autocracy, on surviving Trumpism, very necessary reading now.

Traces of the Ice Age

striationsDon’t you just love these? These grooves are found along the path in the forest of the NYBG, and time and generations of feet have worn them down slightly. They’re glacial striations, gouged out by the rubble on the bottom the ice as it scraped across the hard surface rock.

These can be found in Central Park, too. But not here in the home borough, which is all glacial deposit–made up, come to think of it, with some of that Bronx rock.


IMG_6951Seemingly drilled into the schist of Inwood Hill by some kind of large-bore drill, this is actually a glacial pothole, scoured out by the mighty power of swirling water and abrasive stones during the heady days of the Wisconsin glaciation. The diameter is a little over a foot and a half.

The heights of Inwood, very like a whale from the vantage point of the Hudson, are the northern prong of the Fort Washington Ridge. Geologically, this rock is known as the Manhattan Formation, made of mica and hornblende schist. (“Manhattan’s gneiss, but full of schist” goes the immortal line.) This is the good, hard stuff, the serious, no-nonsense rock, but everything has its weaknesses, and time grinds it all up, as in the mills of the gods.

Sandstone and Basalt

IMG_3353Kind of hot for blogging, wot? Let’s take a dip in the North Sea: this is Greymare Rock, also known as Saddle Rock and the Whale’s Belly, just south of Dunstanburgh Castle. It’s made up of buckled layers of sandstone, the same sandstone used to build the nearby castle. IMG_3345 The castle itself, a ruin now, was built on an exposed ridge of basaltic Whinn Sill, a natural wall to the sea. Brilliant budgeting, that. IMG_3351The pale discoloration in the far distance on the cliff is guano from birds. The cliff hosts a nesting colony of Kittiwakes.

Oh, Schist!

schistI never get tired of quoting that guy in the Times who wrote succinctly that “Manhattan is gneiss, but full of schist.” The bare bones of the little island of Mannahatta are exposed on the upper, upper west side where a ridge of mica schist, the famed Manhattan schist, rises over the flatlands of Harlem. The pictured flank is in St. Nicholas Park, at 137th and Saint Nicholas Ave. The neo-Gothic buildings of CCNY loom above.

That sure looks like rock varnish to me, something more famous in the southwest. Also going on here is sheeting, or contour weathering, a type of rock exfoliation due to the chisel of time and weather.ArtemisiaAnd in a little hollow, a patch of Mugwort (Artemisia)! The stuff grows anywhere. Its roots, like other plants punching into rock, will assist in the weathering away of this rock face over time.


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