Complex sentence: Gray came to the Oregon Country as a lay member of the Spalding-Whitman missionary group, but resigned his position and came to the Salem area in 1842 to work at the Oregon Institute.
Split into simpler sentences: Gray came to the Oregon Country as a lay member of the Spalding-Whitman missionary group. Resigning his post in 1842, he went to the Salem area to work at the Oregon Institute.