NOVEMBEB 3, 1911] 



WISNCE 



613 



reviewed some of his recent observations 

 along the Atlantic and European coasts. He 

 emphasized the point not often brought out 

 that most of our evidence of subsidence is 

 referred to high tide, and that a change in the 

 range of tide may show apparent subsidence. 



Professor Davis was not able to agree with 

 Johnson. He had found sections of as much 

 as twelve feet of salt water peat formed 

 mainly of Spartina patens which only occurs 

 a few inches below high tide and is replaced 

 by fresh and brackish water forms with a 

 very slight elevation, and if the exposure to 

 salt water amounts to more than a couple of 

 hours a day is replaced by another species — 

 Spartina glabra. The occurrence of such de- 

 posits composed almost exclusively of Spartina 

 patens from top to bottom seemed to him to 

 prove almost conclusively a steady subsidence 

 and he presented a bit of evidence for the first 

 time as to the rate thereof. The upper layers 

 of marshes at ISTeponset and Revere crossed 

 by the railroad show for the upper three inches 

 more or less of the peat particles of cinder 

 from the locomotive so that there appears to 

 have been accumulation of something like 

 three inches in the last fifty years or so. 



On Saturday the ferry across Boston Harbor 

 gave an opportunity to see the general physio- 

 graphic location of the Navy Yard bench 

 mark which according to Freeman shows sub- 

 sidence. This is explained by Johnson as pre- 

 sumably due to a higher range of tide owing 

 to the filling of the Back Bay, etc., which once 

 led off the waters. The question as to the 

 effect of wharves and embankments on the 

 high tide was discussed. 



The train gave very good views of sections 

 of drumlins and at Revere Beach, the site of 

 Cherry Island (now entirely washed away) was 

 noted, and the peculiar scallops on the shore. 

 These are explained by Johnson and Lane as 

 due to the waves taking advantage of irregu- 

 larities and in breaking making sidewise 

 fountains, as they may be called, which ex- 

 tending laterally have a limit of breadth de- 

 pending on the height and size of the waves. 

 On the back side of Revere Beach the once 

 forested swamp showed stumps and on top a 



salt marsh turf. New ditches showed the sec- 

 tion of the turf and the creeks which drained 

 the marsh showed how sensitive to level the 

 flora was, because in any small depression 

 there was the Spartina glabra while on the 

 knolls around the stumps was a more compli- 

 cated flora with goldenrod and asters creeping 

 in. The salt water peat had a strong odor of 

 sulphureted hydrogen and the darker peat at 

 the bottom showed brackish water formations. 



Around Oak Island (a large group of trees 

 slightly above tide level) no rim of stumps 

 was seen as would be expected, except a few 

 poorly preserved stumps of oak and hickory. 

 The salt peat was shown to contain only the 

 roots and underground parts of the plant, not 

 the leaves and aerial parts as the fresh water 

 marshes because they were swept bare by the 

 tide. Beneath this part of the marsh was 

 about 9 feet of salt water peat in general and 

 in order to explain it as not due to continuous 

 subsidence Professor Johnson had to explain 

 it as due to subsidence of several feet several 

 thousand years ago followed by an apparent 

 subsidence of a foot or two more recently due 

 to the changes of the ran of tide. The objec- 

 tion to this was that no marked break was 

 found as might be expected. 



In a partly cut away drumlin Professor 

 Perkins recognized some boulders, similar to 

 the Vermont red sandstone, which may be of 

 Cambrian age. 



On the way from Revere Beach to Nahant 

 a brief stop enabled one to see the ripple 

 marks and rills and other phenomena of the 

 Lynn Beach. 



At Nahant was visited another salt marsh 

 which is fourteen feet deep with two feet of 

 sedge and twelve of salt marsh peat. On the 

 golf links relics of stumps were again visible. 

 The beach connecting Bass Point showed the 

 high water scallops once more and Professor 

 Johnson gave an account of their formation 

 and some experiments he had made in pro- 

 ducing artificial scallops.* At low tide this 

 beach is said to show peat passing under it 

 and Professor Johnson explained such peat 



* See Geol. Soc. Am. Bulletin, Vol. 21, pp. 599- 

 624. 



