NOVEMBEB 18, 1010] 



SCIENCE 



723 



the marsh will first be submerged by the high 

 tides and later buried in salt marsh deposits; 

 and so the various evidences advanced in favor 

 of coastal subsidence will be produced without 

 any vertical movement of the land. 



A" valuable demonstration of the importance 

 of this principle has been furnished by nature 

 on a fairly large scale near Scituate. Mass. 

 The " Portland Storm " of 1898 broke through 

 the bar which almost separated the North 

 River marshes and bay from the ocean, 

 thereby allowing a freer access of water to the 

 bay and raising the high tide surface from 

 one to several feet above its former position. 

 Within two years the shores of the marsh were 

 bordered by a zone of dead trees, the width 

 of the zone varying from a few feet to a num- 

 ber of hundred feet and being widest where 

 fresh-water vegetation had formerly en- 

 croached some distance on the marsh surface. 

 To-day the marsh is gradually building up 

 toward the new high-tide level, and one may 

 see an old dyke completely covered with salt- 

 marsh vegetation, and dead trunks of pines, 

 cedars, birches and oaks standing surrounded 

 by the salt grasses. A bathing pool in the 

 North River, formerly of fresh water, is now 

 saline; and the fresh marshes some distance 

 up the river are now being transformed to 

 salt marshes. 



Boston Harbor and the smaller bays and 

 marshes which ramify inland from it have 

 been much altered during the last three-quar- 

 ters of a century. In particular, large areas 

 of bay and marsh have been reclaimed from 

 the sea, thereby decreasing the extent to which 

 tidal waters must spread out after passing 

 through such narrows as that between Boston 

 and East Boston. It is inevitable that such 

 changes should affect the level of the high- 

 tide surface, and perhaps that of half-tide as 

 well. One must doubt, therefore, the validity 

 of evidence in favor of subsidence based on 

 the fact that an accurately established bench 

 mark no longer bears its original relation to 

 tidal heights. 



Both on the Massachusetts and on the Xew 

 Jersey coast conditions favor appreciable 

 changes of high-tide level due to changes in 



the shorelines. In the light of the facts stated 

 above, the evidence of recent subsidence along 

 these coasts thus far presented must be con- 

 sidered inconclusive. That there has been 

 subsidence in the past seems reasonably cer- 

 tain ; but the writer knows of no satisfactory 

 evidence of recent subsidence in these two 

 areas. 



D. W. Johnson 



THE GLACUL ORIGIN OF THE ROXBURY CONGLOM- 

 ERATE 



In England, as long ago as 1855, Sir An- 

 drew C. Ramsay found evidence of glacial 

 action in the Permian rocks of the Midlands. 

 Since that time evidence of the Permian Ice 

 Age has been found in India, Australia, South 

 Africa and South America. 



Dr. La Forge, while engaged in the geo- 

 logical survey of the Boston region, for the 

 United States government, came upon a 

 curious outcrop of the conglomerate known as 

 the Roxbury, at a locality in the town of 

 Hyde Park, south of Boston. Last December 

 we visited this section. Here the rock con- 

 tains pebbles and boulders up to several feet 

 in diameter, largely angular or subangular, 

 scattered rather sparsely through a " pasty " 

 matrix which forms the greater part of the 

 bulk of the rock. There are no traces of bed- 

 ding or of water action during deposition, and 

 Mr. Sayles was so impressed by the resem- 

 blance of the rock to a glacial deposit that he 

 at once suggested the probability of its being 

 unite. Other localities where the rock dis- 

 plays the same characters were visited, but 

 soon a heavy snow-fall prevented any system- 

 atic work until spring, when Mr. Sayles 

 made a careful search at several localities for 

 definite evidence of glacial origin, and se- 

 cured numerous chipped or faceted pebbles, 

 some showing apparent glacial striae. 



More recently, in company with Dr. Ells- 

 worth Huntington, we visited the extensive 

 exposures at the same horizon on the penin- 

 sula of Squantum, in Quiney, southeast of 

 Boston, where the rock is much like that at 

 Hyde Park, but the proportion of pebbles to 

 matrix is greater, the matrix is often more 



