Madison Boulder is made of fine-grained feldspar and larger quartz crystals that welled up under great pressures from a molten mass deep in the earth over 200 million years ago. Upon cooling, the molten rock hardened. Over the millions of intervening years softer materials on the earth's surface were removed by erosion from wind and water. Not so with the granite of New Hampshire, the Granite State!
As recently as 1835, geologists believed that huge boulders like Madison Boulder isolated in their surroundings had been washed to their present locations by great floods which are said to have occurred in ancient times. Today, it is believed that these large boulders, or "erratics," were moved various distances during the last ice age.
Most authorities trace Madison Boulder to the Whitton or White ledges 12.5 and 4 miles respectively, to the northwest. However, a few maintain that the boulder so closely resembles one of the four types of rock that form Mount Willard in Crawford Notch, twenty-four miles to the nothwest, that the ice sheet must have brought it from there. Madison Boulder lies on "glacial drift," unsorted sediments left by the retreating ice sheet.
