Geologically Nantucket is a terminal moraine, a great hill of till which the once all-prevalent glacier scraped from the mainland and dropped where it now lifts clay cliffs and stretches sandy shoals to the warm waves of the Gulf Stream. Bostonians who know their geology should feel at home in Nantucket, for, while it is superficially allied to Cape Cod, the pebbles of the stratified gravel on the north being in a large part derived from the group of granite rocks known on the neighboring mainland, perhaps half of the mass being of that nature, the remainder is of the felsite and felsite-porphyries so common in the region about Boston. Here and there are a few big boulders, believed by geologists to have been dropped by stranding icebergs and without doubt natives of Greenland. The island holds vegetation also imported from far distant areas and established long before man, civilized man at least, came to it. ***** On favored uplands one finds the Scotch heather and he might think it had been brought by the loving hand of some Scotchman were it not for the fact that the earliest settlers found it here. They came, these earliest settlers, in 1659, Thomas Macy and his wife, Edward Starbuck, James Coffin and Isaac Coleman, a boy of twelve, storm-tossed about Cape Cod and over the shoals, all the way from Salisbury. For them the merrymen breakers on the shoals danced as they do for the incomers of today. They were not sailors, not even the master of the ship. Perhaps that is why they kept on to the end of the two hundred-mile voyage. At any rate, they did, and they found the Scotch heather here. Here, too, one finds another strange plant, plentiful over on the sandy peninsula of Coatue, the Opuntia or prickly pear, a variety of cactus common enough in Mexico and portions of our Southwest, but surprising on this island. In these two plants at least east and west stand face to face across Nantucket harbor, the cactus holding the sandspit to the north, the heather on the main island to the south. In April the prickly pear is as ugly as sin to the eye with its lobster-claw growth, uglier still to the hand with its steel-pointed thorns, but later it will put forth wonderful yellow, wild-rose like blooms in rich profusion, making up for all its dourness. Professor Asa Gray, the distinguished botanist of a half century ago, used to say that nothing in the way of plant life could surprise him on Nantucket. Probably this juxtaposition of cactus and heather prompted the feeling.