1913] JOHNSON—COASTAL SUBSIDENCE 459 
near Boston; an explanation which seems hardly competent té 
account for such a widespread phenomenon. More recently 
Davis" of the United States Bureau of Mines, an expert in the 
examination of peat deposits, has placed especial emphasis upon 
that feature of salt marshes described by Mupce, and believes 
that he has found therein a conclusive proof of a gradual sub- 
sidence of the Atlantic coast, probably not faster than a foot a 
century, continuing up to the present time. Others have likewise 
thought that they found in submerged salt peat a proof of recent 
subsidence, and have cited the outcropping of such peat at low 
tide on the seaward side of barrier beaches, bearing the impressions 
of the hoofs of cattle and horses and of wagon wheels, as certain 
proofs of very recent marked subsidence. 
It is well known that the attack of the waves often drives a 
barrier beach inward over the salt marsh. The enormous weight 
of the beach necessarily results in a compression of the peat deposit, 
so that the surface of the latter is exposed near or below low tide 
level on the seaward side of the beach (fig. 4). On the coast near 
Boston a barrier beach has been driven back over a salt marsh 
more than 70 meters in twelve years. Today the former surface 
of the meadow, with the wheel tracks of an old road, impressions 
of horses hoofs, and the stumps of trees which had gained a foot- 
hold on the marsh inside of the beach, are all exposed at low tide 
on the seaward side of the beach. Those who would interpret 
this as a result of coastal subsidence must admit a subsidence of 
perhaps two meters in twelve years, of which there is no corroborat- 
ing evidence whatever. In fact, the bending down of the former 
surface of the marsh is readily apparent where the peat outcrops 
toward the sea; and the fact of extensive compression 1s so 
by two sections taken through the peat deposit; one 1m ——— 
a short distance back of the beach, revealing about he ee 
of relatively soft peat; the other near low tide level, ae 
one meter of very dense, compact, tough peat. The ws ge 
slope of the former marsh surface may be obscured rae (i. 
beach by more recent deposits built up to high tide level (ng- dt 
of Maine. Bull. 376, pee 
Bastin, E. S., and Davis, C. A., Peat deposits ‘on near Boston, an 
Geol. Surv. 19-21. 1909; also Davis, C. A., Salt paren Somme 
its geological significance. Economic Geology 5:625. 1910. 

