Among the early concerns of the nation's founders was the lack of a national prime meridian, required for establishing longitudes on land. In 1804, when Thomas Jefferson began planning the Lewis and Clark Expedtion, he realized the need for the establishment of a single prime meridian to faciilitate mapping of the expanding nation. This book is a history of the meridian marker which becam known as the Jefferson Stone, a replacement granite monument remains today near the Washington Monument.