The peat at Grassy Island proved to be anomalous in having only a top ven- 

 eer of high-tide peat from one to two feet thick. Beneath this is a mass of re- 

 worked peaty materials in which there is a mixture of high-tide species with 

 some rhizomes of mid -tide grasses. The under surface of the veneer of high- 

 tide peat is a fairly even inclined plane sloping downward from east to west. 

 Thus the high-tide peat is thickest on the western shore of the island. This 

 shore is clifflike in formation, with the reworked peat undercut beneath the 

 upper layer of high-tide peat. The east shore of the island is more gently 

 sloping, and is covered with mid-tide grasses in its upper parts. It slopes into 

 a mucky bottom below tide level. The nature of the two peats, and the manner 

 of their deposit, were in part worked out in a nearby marsh which drains into 

 the eastern side of Smith's Cove. Here it was found that the activity of a 

 meandering tidal stream (Shove's Creek), altering its course as the tide levels 

 rose, had formed a "lens" of mixed peat in the zone of the meanders. Apply- 

 ing the principles observed there, it was found that the peat on the west shore 

 of Grassy Island was being eroded away and carried around the ends of the 

 island by tidal and other currents. It was being deposited as the mixed peat on 

 the gently sloping eastern shore. Assuming that this process had been going on 

 for a long time, it was concluded that the island had been changing its geograph- 

 ical position and gradually migrating eastward. By this reasoning the western 

 shore should be the oldest and should have, as it does, the thickest part of the 

 high -tide peat. 



Comparison with a Coast and Geodetic Survey map made in 1875 indicated 

 that the island had been moving its position at approximately seven-tenths of a 

 foot per year. Again assuming that the advance of the tide levels has been fairly 

 constant for a long time, itwas thought that the slope of the undersurface at the 

 high-tide peat (about 10 inches in 200 feet) would be a function of time and the 

 rate of rise. Projecting this plane westward it was found to intersect the bot- 

 tom of the cove near the eastern margin of the main channel of the river, about 

 1000 feet west of the east shore of the island. At the rate of 0.7 of a foot per 

 year, the island would thus have started its migration about IZOO years ago. 

 We have no figures for the contours of the bottom of Smith's Cove as of that 

 time, but estimating that they were then approximately as they are now, the 

 high tides would have begun to inundate the bottom of the cove above the main 

 channel of the river about 1200 years ago. This woiild give an approximate 

 date for the time at which archaeological sites located on the bottom of the cove 

 became uninhabitable. 



Immediately following the time of inundation by high tide, the bottom of the 

 cove must have been covered by a fairly continuous salt marsh. We believe 

 that this marsh was for the most part removed by tidal currents as the water 

 deepened, leaving only the ancestral Grassy Island and perhaps other small 

 pieces of marsh peat which have since disappeared. 



DISCUSSION 



Redfield: I have just one remark to make which has not been mentioned yet 



and is pertinent with regard to the rise in sea level. That is 



117 



