Vast salt marshes, ancient grasslands, lush forests, pristine beaches and dunes, and copious inland waters, all surrounded by a teeming sea. These are probably not the first things you imagine when you think of Long Island, but just beyond its highways and housing developments lies a stunning landscape full of diverse plant and animal life.    Combining science writing, environmental history, and first-hand accounts from a longtime resident,  At the Glacier's Edge  offers a unique narrative natural history of Long Island. Betsy McCully tells the story of how the island was formed at the end of the last ice age, how its habitats evolved, and how humans in the last few hundred years have radically altered and degraded its landscape. Yet as she personally recounts the habitat losses and species declines she has witnessed over the past few decades, she describes the vital efforts that environmental activists are making to restore and reclaim this land-from replanting salt marshes, to preserving remaining grasslands and forests, to cleaning up the waters.  At the Glacier's Edge  provides an in-depth look at the flora, fauna and geology that make Long Island so special.