460 MYRON L. FULLER 
Rate of settling.— Recently, in connection with professional 
work for the Metropolitan Water Board of Massachusetts, Pro- 
fessor W. O. Crosby has incidentally had occasion to determine 
the rate of settling of the finer portions (2. ¢., quartz-flour) of both 
the till and the stratified drift. No definite maximum limit has 
ever been fixed for the grains of quartz flour, but in the experi- 
ments in question this name was applied to that portion passing 
through a sieve of 170 meshes to an inch. The larger grains are 
about 34, of an inch in diameter. 
In the experiments, the results of which Professor Crosby has 
kindly placed at my disposal, 5 grams of the quartz flour were 
introduced at the top of a half-inch tube containing five feet 
of water. The time of settling was then taken. The results 
showed that fully 75 per cent. of the material settled within 
thirty minutes from the time of insertion, and in the majority of 
cases none whatever remained in suspension at the end of sixty 
minutes. In other cases a distinct turbidity, probably due to 
true clay, was still noticeable at the end of this time. This was 
determined by filtering and weighing, the amount varying from 
a mere trace up to IO per cent. 
The results show that even in fresh water the settling of 
quartz flour is very rapid, the greater part settling at a rate of at 
least ten feet per hour. In the inclosed bay in which the Bar- 
rington clays were deposited the water was salt, or at least 
decidedly brackish, and the rate of settling must have been much 
increased, especially in the case of the finer material, which, 
according to W. H. Brewer, will settle as much in salt water in 
thirty minutes as it would in as many months in perfectly pure 
water.*. There can be no reasonable doubt, then, that practically 
the entire amount of sediment brought in by the glacial stream 
was deposited within the inclosed bay. 
Statement of problem and results.— During a certain stage of 
the ice retreat from the region of Narragansett Bay, the area 
now covered by the Barrington clays stood at a level some forty 
feet below that at present existing, and was covered by a body 
Am: J. Sci., TI]; 20, p. 4: 
