258 (Review 0/ liecenl Geological Literature. 
sion of the various species, referred to the different provinces, show- 
ing an extensive Cretaceous formation along the Atlantic coast of 
South America. 
Preliminary report on sea-coast sivatnps of the eastern United States. Bj 
N. S. Shaler. Pages 353-398. (Accompanying the sixth annual report 
of the director of the U. S. geological survey.) 
The most noteworthy features of our Atlantic coast from New Hamp- 
shire southward are its beaches lying commonly one to five miles outside 
the shore of the mainland, and its salt marshes or swamps which are 
formed in the shallow water thus enclosed. They remind one of the 
barrier coral reefs of tropical shores, and the author finds in them an al- 
most equally interesting field of geological study. 
Where deep water reaches to the coast and fills its indentations, as 
along the hilly and partly mountainous coast of Maine, these sheltering 
beaches are wanting or very scantily developed, and swamp deposits are 
limited to estuaries and narrow margins of the most shallow and pro- 
tected bays and inlets. In marked contrast with this, on the south side 
of Long Island and from New Jersey to Florida, the very gentle slope of 
the coastal plain in its descent beneath the sea-level causes the formation 
of the beach to take place several miles off shore, where it extends nearly 
continuously along this distance of athousand miles. Along the portions 
of the coast most favorable for its formation it is interrupted only by 
gaps which are maintained by the outflow from rivers and the flow and 
ebb of tides. 
On a moderately hilly coast, like that of Massachusetts, when the sea 
has been shallowed by the accumulation of sediment so that the space 
between the capes of a bay is brought within about twenty feet of the 
surface at the time of low tide, the conditions are favorable for the closure 
of the inlet by a barrier beach. In heavy storms the waves mount too 
high to pass over the shallow without breaking. The forward motion of 
the wave is arrested, aud the detritus which it was virging forward falls 
upon the bottom, until gradually a ridge of beach gravel and sand is 
built up to the level of high water. Protected behind the beach, the 
swamp deposits are formed chiefly of the fine sediments brought in by 
the tides. The dense growth of eel-grass covering the bottom favors 
this deposition of sea-mud up to the level of low tide, and forms the 
lowest bed of the swamp. Between this marine vegetation and that of 
the shores a zone of mud flats, laid bare at low tide, is built up more 
slowly until it reaches sufficient light to permit the growth of the marsh- 
grass and other shore vegetation which can endure at most only a sub- 
mergence of a few feet at high tide. These form respectively the mid- 
dle and upper beds of the sea-coast swamp, the surface of which is thus 
raised nearly to the level of the highest tides and then supplies crops of 
marsh hay. 
The tide flows in and out by very irregularly winding and branching 
channels, and there is hardly an acre that is without one of these water- 
ways. Its steep sides and tortuous course show its constant battle with 
