When John Muir was a student in the University of Wisconsin he was a frequent caller at the house of Dr. Ezra S. Carr. The kindness shown him there, and especially the sympathy which Mrs. Carr, as a botanist and a lover of nature, felt in the young man's interests and aims, led to the formation of a lasting friendship. He regarded Mrs. Carr, indeed, as his "spiritual mother," and his letters to her in later years are the outpourings of a sensitive spirit to one who he felt thoroughly understood and sympathized with him. These letters are therefore peculiarly revealing of their writer's personality. Most of them were written from the Yosemite Valley, and they give a good notion of the life Muir led there, sheep-herding, guiding, and tending a sawmill at intervals to earn his daily bread, but devoting his real self to an ardent scientific study of glacial geology and a joyous and reverent communion with Nature. - Summary from the preface of the book.