There are, in fact, quite a few similarities between the poems "The Chambered Nautilus" by Oliver Wendell Holmes and "Thanatopsis" by William Cullen Bryant, but there are also some significant differences. Each poem confronts a fear of mortality and looks to Nature for insight into human nature, though the poems have differing ideas about the soul and the body.
"Thanatopsis" means "meditation on death," and much of the poem is just that. The speaker of the poem begins by telling the reader both joy and comfort can be found by observing Nature. The speaker regards Nature in a general sense, describing valleys, mountains, the ocean, and the woods. He explains to the reader that fear of death is unnecessary, since everyone has to die sometime, and he asks the reader to find consolation in the fact that all men and women will become part of Nature again as their bodies become one with the earth. For this speaker, comfort can also be found in the fact that the dead inhabit every corner of the world and, therefore, he will join a great multitude of spirits when he dies.
While "The Chambered Nautilus" focuses on one specific part of Nature--the shell left behind after the death of a mollusk--the speaker finds a similar type of comfort when faced with mortality. For the speaker of this poem, however, the spirit and the body are two very different things. While the body will be left behind, as the nautilus was, the spirit has the chance to ascend to heaven. The nautilus thus becomes a symbol of the spiritual journey. As the mollusk outgrows each chamber, he builds a new one. Similarly, as a person grows in nobility, he outgrows his figuratively small former life until, through death, he escapes the confines of his body.