Development of coastal marshes during the Holocene submergence of the northeastern United States seems to have been episodic. Radiocarbon dating of the modern marshes indicates that they were generally established within the past 3,000 yr. Initiation of marsh growth was probably related to the marked slowing in the submergence rate that took place in the area about 3,000 to 4,000 yr ago. On the basis of the few available dates of marsh peats from the inner continental shelf, we suggest that previous episodes of marsh growth took place at about 4,700, 5,600, 6,600, 7,700, 8,200, and 8,600 radiocarbon yr ago. These times of marsh growth seem to coincide with proposed times of negative sea-level oscillations, cool climate, and glacial advances. If these oscillations of sea level are climatically controlled, then the data suggest an approximately 1,000-yr cycle of climatic change.