This high rocky region of around 1,000- to 2,000-feet elevation is underlaid by ancient sandstone that was formed some hundreds of millions of years ago in the deepest ocean trenches, but which was forced up from those trenches during continental drift to form mountainous ridges. Originally higher than the Himalayas, these mountains have eroded away over millions of years to what are now known as the Taconic Mountains and the Rensselaer Plateau.
The Rensselaer Plateau is distinguished by a particular kind of sandstone called Graywacke, which consists of crystalline and lithic fragments set in a compact clay-fine matrix. Unlike typical sedimentary sandstone, which is formed by sand settling in undisturbed layers, Graywacke contains a jumble of both older and newer layers, formed when volcanic forces shuffled the older layers above the newer ones.
Because the chemistry of Graywacke tends to be acidic rather than basic, we plant people in the Thursday Naturalists were curious about what flora flourished among such a substrate, and we chose to explore a small nature preserve near Stephentown called the Robert P. Ingalls Nature Preserve. Named for a noted expert on Rensselaer County flora, this preserve features an easy loop trail that follows a pretty creek through a mixed hardwood/conifer forest.
Lying about this woods were many examples of Graywacke, displaying streaks of crystalline rock mixed throughout rock of a finer texture.
A completely unexpected find was a patch of the pretty moss called Rhodobryum roseum growing on the bank of the creek. Because this is a moss that prefers a basic, rather than acidic, substrate, we were quite surprised to find it here in this woodland underlaid by acidic rock. But then we noted that the moss was growing on a tree root rather than on rock, so perhaps that was a factor.
Update: I received a note from my friend Bob Duncan with some interesting information about this particular moss. I quote him directly here (and I also corrected my spelling!):
Hi, Jackie. I decided to catch up on your blog today and enjoyed your last two. Thought I should let you know Rhodobryum is spelled with a 'y' . Also it appears the plant we have is actually R. ontariense. I learned it as R. roseum but a paper published in 1972 established that there are actually two species with overlapping global ranges that are separable by very minor characters. When Crum and Anderson published 'Mosses of Eastern North America' in 1981 they admitted that the plants in our area are R. ontariense but felt the differences were trivial and felt the subject needed more study so they continued using the name R. roseum. I think maybe they also liked that name and didn't want to give up a name they had probably been using for fifty years!
Another feature of the Ingalls Preserve was the presence of enormous White Pines, some with straight trunks of substantial girth, others with split trunks that indicated a long-ago infestation by Pine Weevils. As our friend Kathy (shown here leaning against one double-trunked pine) explained to us, whenever we find a pine trunk the splits at just about nine feet above the ground, it is almost certain to be the result of the action of these weevils. Kathy said she learned this on an outing led by noted terrestrial ecologist and forest historian Tom Wessels.
The trail through the Ingalls Preserve was short enough that we still had lots of time to visit another nearby site, a State Forest Preserve tract adjoining the Cherry Plain State Park near the Massachusetts border. Here, we walked a beautiful woodland trail along a tumbling creek until we reached the site of a splendid waterfall.
Although the day was chilly, the sun-warmed banks by the waterfall made for a wonderful spot for a streamside picnic.
Since we were still in the area of the Rensselaer Plateau, we expected to find more examples of Graywacke, and we were not disappointed. This particular boulder had cracked open to reveal the presence of translucent crystalline fragments within the encasing fine-grained sandstone.