612 



SCIENCE 



[N. S. Vol. XXXIV. No. 879 



overwash gravel plain from the ice but a 

 boulder of the weathered diabase and an un- 

 conformity were seen — ^the upper layer being 

 more oxidized and leached, the lower showing 

 more cross-bedding with a considerable 

 amount of hornblende with the quartz, sug- 

 gesting a beach deposit lying on top of the 

 gravel plain. At No, 69 the underlying slate, 

 not smooth and glaciated, was shown. 



At the Holland St. quarry Professor 

 Palache showed veins (confined almost to the 

 diabase) in which calcite, quartz, siderite 

 and almost microscopic anatase and other 

 minerals have been found. 



Passing over College Hill other sections of 

 till above the 35-foot line and of shearing and 

 jointing in the slate, which on Quincy Street 

 dips nearly vertically and has numerous small 

 faults, were shown. The extensive view from 

 the reservoir shows the peneplain of the 

 Middlesex Fells, the lower land of the Boston 

 Basin, the glacial outwash gravel plain of 

 Arlington, a quarry on the Fellsway in felsite 

 with calcite and specular hematite and barite 

 in veins (later visited), the drowned valley 

 of the Mystic with its salt peat marshes and 

 numerous drumlins. Descending to this val- 

 ley Dr. Davis pointed out the freshening of 

 the Spartina patens salt marsh indicated by 

 the invasion of various fresh water plants. 

 This has all happened in three or four years 

 while the dredge has thrown up signs of fresh 

 water peat at a considerably lower level than 

 the sea level. 



Next were visited the Medford diabase 

 weathering on Governor's Avenue and Fella- 

 way quarry and the Wellington clay beds. 

 Here were found two distinct beds of clay 

 with a sand layer between, and above a bed of 

 gravel which Gulliver showed by the per cent, 

 of angular pebbles was undoubtedly glacial 

 outwash. Barton called attention to faulting 

 in the sand and cementing of the sand into 

 sandstone and conglomerate. The Mystic 

 valley is, then, largely filled by this gravel 

 plain and on top of it is the marsh deposit 

 of irregular thickness, sometimes not very 

 deep. In other hollows of the gravel plain 



we find (a) fresh water peat, with sticks and 

 leaves, 10 feet; (6) fresh water swamp bed 

 with stumps; (c) brackish water swamp, 1 ft.; 

 id) thin high tide Spartina patens salt water 

 deposit. Stumps of a former pine forest were 

 very conspicuous near the margin and were 

 connected with a fresh water peat layer 

 pointed out by Professor Davis, on which grew 

 a salt marsh. The evidence that this pine 

 forest had been invaded by the salt marsh was 

 not challenged by any one and the freshness 

 of the pine stumps showed that it was rela- 

 tively recent, as D. White emphasized. 



Professor D. W. Johnson, however, pointed 

 out in the discussion which took place that 

 evening in the Barnum Museum at Tufts 

 College that certainly at Scituate and in 

 some other cases such invasion of salt marsh 

 was due to an increase in tidal range with- 

 out any subsidence of the land, and that 

 if the tidal range outside a barrier beach was, 

 say 20 feet, in going up a stream that range 

 would gradually diminish, so that if a beach 

 were broken through, or driven back, or in 

 any way the access of water made more free, 

 the increase in tidal range would taTce place 

 and produce an effect of apparent subsidence, 

 while mean sea level might not differ. 



The same evening Professor Fernald, of 

 Harvard, gave an interesting account of the 

 flora of Newfoundland,' which while it has 

 Labrador and Polar plants, has very few of 

 the Canada flora only seventy miles away 

 across the Gulf of St. Lawrence but has a 

 large percentage of plants of the sandy south- 

 ern coastal plain from Cape Cod south. There 

 is a bar between Newfoundland and Cape 

 Cod which might have been uncovered when 

 the water of the ice sheet was taken from the 

 ocean. 



Professor Johnson gave the account of the 

 development of Nantasket which had already 

 been visited in an earlier excursion' and 

 pointed out with very strong argument that 

 the level had remained fixed within a couple 

 of feet for over a thousand years — probably 

 several thousand — derived therefrom. He also 



' Described in the July Bhodora. 



° Science, 1906, p. 155. 



