existing Physical Causes during stated Periods of Time. 29 
suspension to rivers flowing directly into the sea.* If this area 
be annually reduced in level at the same rate as the district 
through which the Mississippi flows, then the mean level of the 
land on the globe would be reduced 3 feet in 54,000 years, and 
' consequently the level of the ocean raised 1 foot in the same pe- 
tiod by means of the detritus suspended in river-water poured 
into the ocean. 
What this would annually amount to, for old maps and charts are 
hardly accurate enough to represent the waste of cliffs by breaker- 
action even within the last 100 years. Capt. Washington has, 
however, published a reportt which gives an account of the en- 
croachment ef the sea at intervals on one part of the Suffolk coast. 
This will give a general idea of the contribution of detritus that 
may beobtained from some points of a coast-line. The following 
statements are collected from Capt. Washington’s Report on Har- 
oe Fale in 1844, from which also the figures 4, 5, 6, 7, are 
copied, 
The cliff on the western side of the harbor is about 1 mile 
long and 40 feet high, and the encroachment of the sea appears 
to have been at the rate of 1 foot per annum between the years 
1709 and 1756, so that the annual supply of detritus was equal to 
40 cubic feet for each foot of frontage. Between 1756 and 1804 
the advance increased to nearly 2 feet per annum; so that the 
annual removal of cliff amounted to nearly 80 cubic feet for each 
foot of frontage. 
Between 1804 and 1844 the encroachment of the sea averaged 
10 feet per annum, and the annual removal of detritus must have 
amounted to 400 cubic feet for each foot of frontage. It was 
during this latter period that extensive dredging for cement stone 
took place at the base of the cliff. 
On the eastern side of the harbor events of an opposite char- 
ons on this 
3 
+ Tidal Harbors’ Commission, 

