Stories in Stone Read Free Page A

deposit layer upon layer of sand and silt. Dinosaurs plod through the wet sediments leaving behind thousands of tracks. Sediments
     and tracks harden into sandstone. To understand why dinosaurs inhabited that valley, why quarries occur where they do, and
     why brownstone was a good building stone, however, requires adding a few more details.
    The valley where the dinosaurs roamed sat in the middle of the supercontinent of Pangaea, which like a giant puzzle, consisted
     of many smaller pieces of land. The northern portion, called Laurasia, included Siberia, Europe, and North America. Antarctica,Africa,
     South America, India, and Australia, collectively known as Gondwana, formed the south part of Pangaea and extended down to
     the South Pole. All was not right, however. As that great geologist Bob Dylan sang, “He not busy being born is busy dying,”
     and Pangaea began to break up.
    At least fifteen rift valleys, or basins, opened as North America,Africa, and South America pulled away from one another.
     The individual basins stretched from Alabama to the Bay of Fundy. Streams from adjacent hills and mountains began to carry
     sand and silt into the basins, including one where the Connecticut River now flows, from about modern-day Amherst, Massachusetts,
     to New Haven, Connecticut. Geologists call this lowland either the Connecticut River valley or the Hartford Basin.
    Between about 220 and 195 million years ago, this valley lay about ten to fifteen degrees north of the equator, roughly the
     same latitude as present-day El Salvador. Dry and warm with an ecosystem of ferns, cycads, and conifers, the lowland received
     less than twenty inches of rain per year, mostly as seasonal monsoons. A variety of small dinosaurs, about six feet tall and
     shorter, ten-foot-long amphibians, and fish-eating crocodilelike animals inhabited the valley.
    And then, as the continents continued to pull apart, Earth’s crust thinned and the Hartford Basin ripped open, like an overstuffed
     sausage. Black lava spread from swarms of fissures in Connecticut and all of the rift valleys that stretched for a thousand
     miles along the eastern margin of North America. With a consistency of ketchup, the basalt flowed thousands of yards per day.
     In addition to wreaking havoc on the landscape, the viscous basalt spewed out trillions of tons of sulfur dioxide and carbon
     dioxide, generally making the planet an unpleasant place for any species that liked clean air.
    Geologists speculate that this worldwide flood of basalts may have contributed to a mass extinction of 50 percent of planetary
     life, including a diverse group of carnivores and herbivores, generally bigger and badder than dinosaurs who lived at the
     time. With their competitors out of the way, dinosaurs, which had first evolved about 30 million years earlier, reacted quickly
     and doubled in size. They also began to evolve into the myriad species that dominated Earth for the next 140 million years.
     Within twenty-five thousand years of the extinction, new forms had emerged including Anchisaurus , a long-necked herbivore, and twenty-foot-long predators such as the double-crested Dilophosaurus , one of the stars of Jurassic Park . 10 They had taken over from slim, three-foot-long plant eaters and similarly sized meat eaters. Nowhere on the East Coast is
     this record of dinosaur ascendancy better recorded than in the fifteen thousand feet of sediments that accumulated in the
     Connecticut River valley.
    Of all the rock that formed in the valley, the thickest,youngest, and most important to the brownstone story is the Portland
     Formation. Named for its main point of origin—the town of Portland, Connecticut—it is the rock unit that provided the building
     blocks for most of the brownstone row houses of New York and Boston. The stone formed very rapidly, in just a few million
     years, as streams carried sediments out of the surrounding highlands and into a valley of lakes, floodplains,