This particular sill came into the earth about two miles below the surface, Kleinspehn remarks, and she smacks it with the sledge. An air horn blasts. The passing tires, in their numbers, sound like heavy surf. She has to shout to be heard. She pounds again. The rock is competent. The wall of the cut is sheer. She hits it again and again-until a chunk of some poundage falls free. Its fresh surface is asparkle with crystals-free-form, asymmetrical, improvisational plagioclase crystals, bestrewn against a field of dark pyroxene. The rock as a whole is called diabase. It is salt-and-peppery charcoaltweed savings-bank rock. It came to be that way by cooling slowly, at depth, and forming these beautiful crystals. “It pays to put your nose on tl1e outcrop,” she says, turning the sample in her hand. With a smaller zakelijke energie hammer, she tidies it up, like a butcher trimming a roast. With a felt-tip pen, she marks it “i.” Moving along the cut, she points out xenoliths-blobs of the country rock that fell into the magma and became encased there like raisins in bread. She points to flow patterns, to swirls in the diabase where solidifying segments were rolled over, to layers of coarse-grained crystals that settled, like sediments, in beds. The Palisades Sill-in its chemistry and its texture-is a standard example of homogeneous
magma resulting in multiple expressions of rock. It tilts westward. The sill came into a crustal block whose western extremity-known in New Jersey as the Border Fault-is thirty miles away. As the block’s western end went down, it formed the Newark Basin. The high eastern end gradually eroded, shedding sediments into the basin, and the sill was ultimately revealed-a process assisted by the creation and development of the Hudson, which eventually cut out the cliff side panorama of New Jersey as seen across the river from Manhattan: the broad sill, which had cracked, while cooling, into slender columns so upright and uniform that inevitably they would be likened to palisades. In the many fractures of these big roadcuts, there is some suggestion of columns, but actually the cracks running through the cuts are too various to be explained by columnar jointing, let alone by zakelijke energie vergelijken the impudence of dynamite. The sill may have been stressed pretty severely by the tilting of the fault block, Kleinspehn says, or it may have cracked in response to the release of weight as the load above it was eroded away. Solid-earth tides could break it up, too. The sea is not all that responds to the moon. Twice a day the solid earth bobs up and down, as much as a foot. That kind of force and that kind of distance are more than enough to break hard rock. Wells will flow faster during lunar high tides.