The coast of the state of Maine is one of the most irregular in the world. A straight line running from the southernmost coastal city to the north- ernmost coastal city would measure about 225 miles. If you followed the coastline between these points, you would travel more than ten times as far. This irregularity is the result of what is called a drowned coastline. The term comes from the glacial activity of the ice age. At that time, the whole area that is now Maine was part of a mountain range that towered above the sea. As the glacier descended, however, it expended enormous force on those mountains, and they sank into the sea. As the mountains sank, ocean water charged over the lowest parts of the remaining land, form- ing a series of twisting inlets and lagoons of con- torted grottos and nooks. The highest parts of the former mountain range, nearest the shore, remained as islands. Mt. Desert Island is one of the most famous of all the islands left behind by the glacier. Marine fossils found here were 225 feet above sea level, indicating the level of the shore- line prior to the glacier. The 2,500-mile-long rocky and jagged coastline of Maine keeps watch over nearly two thousand islands. Many of these islands are tiny and uninhabited, but many are home to thriving communities. Mt. Desert Island is one of the largest, most beautiful of the Maine coast islands. Measuring 16 miles by 12 miles, Mt. Desert was essentially formed as two distinct islands. It is split almost in half by Somes Sound, a deep and narrow stretch of water, seven miles long. For years, Mt. Desert Island, particularly its major settlement, Bar Harbor, afforded summer homes for the wealthy. Recently though, Bar Harbor has become a burgeoning arts commu- nity as well. But, the best part of the island is the unspoiled forest land known as Acadia National Park. Because the island sits on the boundary line between the temperate and sub-Arctic zones, the island supports the flora and fauna of both zones as well as beach, inland, and alpine plants. It also lies in a major bird migration lane and is a resting spot for many birds. The estab- lishment of Acadia National Park in 1916 means that this natural reserve will be perpetually avail- able to all people, not just the wealthy. Visitors to Acadia may receive nature instruction from the park naturalists as well as enjoy camping, hiking, cycling, and boating. Or they may choose to spend time at the archeological museum, learn- ing about the Stone Age inhabitants of the island. The best view on Mt. Desert Island is from the top of Cadillac Mountain. This mountain rises 1,532 feet, making it the highest mountain on the Atlantic seaboard. From the summit, you can gaze back toward the mainland or out over the Atlantic Ocean and contemplate the beauty created by a retreating glacier. Which of the following statements best expresses the main idea of the fourth para- graph of the selection?