1913] JOHNSON—COASTAL SUBSIDENCE 457 
essentially the same conditions developed on a small scale ar 
occasionally encountered on our coast. | 
Evidently the fresh peat cannot have formed in its present 
position, exposed to marine action. Indeed, it has been argued 
that such peat containing upright stumps cannot form in depres- 
sions below high tide level back from the shore line because the 
level of the ground-water would cause such depressions to contain 
ponds of water in which trees would not grow. Hence it is con- 
cluded that submerged fresh peat is a proof of recent coastal 
subsidence. This conclusion seems to me open to criticism on 
several grounds. In the first place, “floating bogs’ formed of 
sphagnum and carrying trees of considerable size upon them some- 
times cover the surfaces of ponds. The sinking of such a bog, as 
the trees increase in size or as new material is added to its upper 
surface, would carry upright stumps down below sea-level. Decom- 
position of bogs to produce such a semi-liquid mass as is often 
found under their surfaces might permit stumps to sink slowly to 
the bottom and remain upright there. The possibility of some 
such history for a peat bog encroached upon by the sea must be 
definitely excluded by those who would employ these bogs as a 
proof of coastal subsidence. In the second place, it should be 
noted that the lower portions of such bogs may be of very great 
antiquity; even if they formed above sea-level and were carried 
downward by subsidence of the coast, this event may have taken 
place many thousands of years ago. Hence such submerged bogs 
should not be offered as a proof of recent subsidence (within nie 
last 2000 or 3000 years), as has so often been done. In the ne 
place, when such a bog is encroached upon by the sea, the shbegha 
the ground-water table in the bog, formerly at or near its get 
-is rapidly lowered. Near the seaward margin of the ee : : 
ground-water table may decline to mean sea-level; and, wee e 
the margin, to low tide level when the tide is out. As a res = 
this removal of water, the surface of the bog 1s rapidly pai me 
carrying down with it trees which are-killed by exposure to = 
tide (fig. 3). How extensive such a settling of tet itifical 
is suggested by fig. 5, which represents the result of an is 
lowering of the ground-water level. Furthermore, the # 
