40 ROYAL SOCIETY OF CANADA 
to cross by means of a regularly constructed and regularly maintained 
foot path. To-day the tide enters but a short distance into the cove, 
the marsh grass has practically disappeared, and alders, sedges and other 
forms of vegetation have taken its place. At the upper end of the cove, 
sweet grasses are already making their appearance. 
In all such cases it is to be observed that the area in question is 
wholly protected from direct wave action, and so, from erosion. To the 
natural process of tidal silting which would progress very rapidly under 
such favourable conditions, there is joined a very rapid growth of vegeta- 
tion which not only adds to the silt by its abundant remains, but by 
virtue of its mass of roots and tangled stems it serves to catch and retain 
a large amount of material brought down into such basins as the result 
of surface wash. The net result to be looked for under such circum- 
stances, is a rapid filling up of the cove at a rate which we should expect 
to proceed faster than that at which depression of the whole area is 
developed. While at first sight, therefore, such formation of sweet 
meadows might be interpreted as evidence of elevation, they are, in 
point of fact, proof of a precisely contrary result. 
Determination of Time Periods for Marsh Growth. 
From the considerations with which we have thus far been con- 
cerned, it would seem possible to utilize our knowledge of the growth 
of the Kittery and York marshes with respect to a determination of 
(1) the whole time period occupied, and (2) the rate at which subsidence 
has developed or is now proceeding. 
It appears from the evidence afforded by the submerged cañons 
of the Atlantic coast, that depression has been in progress since Pliocene 
time, and that the present horizon of the coast line is the general 
expression of a subsidence which has been developed through a series 
of vertical oscillations. It follows from this that the level of the York 
bog may have been subject to a series of elevations and depressions 
which, with accompanying submergence alternating with drainage, 
might be taken as a means of explaining some of the peculiarities of 
its structure. On the other hand, if it can be shown that the entire 
history of the bog lies within a sufficiently short period of time to agree 
with a period of elevation or a period of depression only, such explana- 
tion would not be valid, but that already offered must be regarded as 
the correct one. 
Along the same coast line, and more especially in exposed localities 
within Portsmouth Harbor, instances of recent erosion are to be met 
with. These have involved the removal of large quantities of loose rock 
within the memory of men now living. The material thus removed 
