Portland Sandstone: A Flawed Local Favorite
by Robin Hazard Ray
Orchis Path near the apex of Mount Auburn Cemetery is a small-scale rock-and-mineral showcase. There you can find the enormous rose-quartz boulder than marks the family plot of George Sands, a local merchant in the memorial business. The Wigglesworth family plot provides a splendid display of elegant, if weathered, Victorian monuments in Italian marble.
There too we find a stone memorial that is not doing very well. The gravesite of Lucy Orne Bowditch (1816–1885) and her husband J. Ingersoll Bowditch (1806–1889) is marked by a table tomb in poor condition [see photo above]. While Sand’s rose quartz monument and the Quincy granite urns that adorn the Bowditch lot will persist almost unchanged for another thousand years, Bowditch’s handsome monument is not faring nearly as well. Parts of the reddish-brown stone pillars that uphold the flat memorial slab have dissolved away, flaking onto the ground below. Other monuments made of this brown stone, including the grand mausoleum of the Cabot Lodge family on Auburn Lake, are in a similar condition.
What is this sandstone, and why was it chosen for such high-profile monuments, despite its obvious faults?
Geologists call this stone the Portland arkose or sandstone after its type location in Portland, CT, adjacent to the Connecticut River south of Hartford. The stone, of Lower Jurassic age (ca. 190–182 million years old), crops out over a north–south stripe of territory from Long Island Sound to the Deerfield, MA, area. It was quarried not only in Portland but at numerous locations up the Connecticut River Valley, including East Longmeadow, MA, and Rocky Hill, CT.
The Portland sandstone is the remaining evidence of a plate-tectonic event in which the New England region suffered a “failed rift.” Massive forces in the Mesozoic era were pulling the local terrane in two different directions (eastward and westward), causing it to break along a plane weakened by earlier geologic events. The rifting allowed the rise of hot magma from the earth’s interior to the surface, with volcanoes spewing ash and lava up and down what is now the Connecticut River Valley. This volcanism in the Triassic period (ca. 252–200 million years ago), just before the Jurassic, left hard evidence such as the Hitchcock and Holyoke basaltic formations in west-central Massachusetts and East and West Rock in New Haven.
Unlike the rift that today slowly rends Africa from Asia along the arm of the Red Sea, the Connecticut River rift never quite materialized. The geometry of the tectonic plates shifted again, and the two sides of the rift stopped moving in opposite directions. The volcanism died down, and gradually the marshy red deposits along the river valley were buried and consolidated into stone.
If you take a close look at the Portland sandstone, you will see the glitter of fragmented micas, which are layered “sheet silicate” minerals with a flexible, almost plastic texture. These flat, shiny minerals are derived from the volcanic source-rocks. Micas are not particularly stable, especially in damp environments; usually they quickly degrade into dull-colored clay minerals such as chlorite, illite, and kaolinite, losing their brightness. Their sparkling presence in the Portland stone indicates that they were buried quickly, in a torrent of sediment pulsing down from an ancient hillside in an alluvial fan, rather than spending extended time exposed to air and water.
Each grain of mica represents a tiny plane of weakness in the sandstone, as exposure to the elements gradually degrades it to weak clay. The battered columns of the Bowditch table tomb—and the chipping front steps of countless “brownstone” row houses in New York City made from Portland sandstone—show that time and chemistry is catching up with this quarry product.
Yet, viewed from a distance, you can see why grieving families might choose the Portland stone over other, more robust alternatives. Its brown color looks almost like wood or soil, giving a warmer cast to the monument than would a cold gray granite or a ghostly white marble. In sunlight, the micas glitter, lending the stone a shimmer than you will not find elsewhere.
For its earthy color and textured surface, the Portland sandstone was beloved by architects of the nineteenth and early twentieth century, especially those who championed the rustic aesthetic of the Romanesque. H. H. Richardson (1838–1886) made liberal use of the stone in landmark buildings such as Trinity Church in Boston’s Copley Square and the Ames Free Public Library in North Easton, MA.
The Portland sandstone quarries are closed now. Some, like the one in East Longmeadow, are completely overgrown and difficult to locate. But if you find yourself with an afternoon to spare, you can easily drive from the Boston area to the type location and largest quarry at Portland, CT, which is now an attractive riverside park. Shoddy though it is as a building or funerary material, the brownstone does kind of grow on you.