114 PROCEEDINGS OF THE BOSTON MEETING 



FIELD EXPERIMENT IN I808TA8Y 

 BY C. W. BROWN 



i'Ahstract) 



A common experience in engineering when a railroad fill is placed upon 

 swamp or mud, is a resulting isostatic readjustment of material about fill, 

 which may correspond in part to some of the phenomena attending surficiai 

 change of load on the earth. 



Presented without notes, with lantern-slide illustrations. 



Discussion 



Prof. W. M, Davis pointed out that the railroad embankment and the ad- 

 joining uplifted tidal flats described by Professor Brown were not altogether 

 homologous with isostatic highlands and lowlands of the earth. The isostasy 

 of the earth's crust involves the following changes of conditions : Given a low- 

 land which is in isostatic adjustment — that is, its mass to a depth of about 

 70 miles is such that any column of it is of a standard value. Now, if that 

 lowland suffers deformation, so that it becomes a mountainous highland aver- 

 aging two miles in elevation, any column of it will then be 72 miles high above 

 the level of compensation ; yet this column will have no greater mass — that is, 

 it will weigh no more — than did the 70-mile column before uplift. Still fur- 

 ther, the highland will in time be worn down to a lowland by the removal of 

 its extra height of two miles. Nevertheless, after this removal the remaining 

 70-mile column will still have the same standard mass or weight as the original 

 70-mile column and as the mountainous 72-mile column. The best explanation 

 of this anomalous condition is due to the late George F. Becker, who suggested 

 that in the change of the initial lowland to the mountainous highland the gain 

 of height is largely due to lateral crushing, whereby the whole mass is so 

 shattered that the empty spaces of its shattered structure will be about 3 per 

 cent of its volume, as a result of which its height of 70 miles will be increased 

 to a height of 72 miles, but its mass will be the same as before. Then, during 

 the erosion of the extra two miles at the top of the column, the empty spaces 

 beneath will be filled up by new material, presumably from deep within the 

 earth : and, thus resolidified, the original weight of the column will be restored. 



POST-GLACIAL RIVER CHANGES IN RHODE ISLAND AND CONTINENTAI TILT 



BY C. W. BROWN 



{Ahstract) 



Decided diversions of river courses at river mouths in unconsolidated ma- 

 terial in similar directions indicate continental uplift with relief of ice-load. 



Presented without notes, with lantern-slide illustrations. 



Discussion 



Prof. J. B. WooDWORTH remarked that he found that the streams described oh 

 the west side of Narragansett Bay displayed adjustments to ice-fronts marked 



