104 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
IV. 
Conclusions regarding the Forms and Structure of the Stone 
Reefs. 
I. Тнв Forms or тнв STONE Reurs. 
It is often stated by writers on the stone reefs of Brazil that they are 
perfectly straight. Liais himself, who saw those at and immediately 
south of Pernambuco, says, “jamais la récif ne se courbe.” To be very 
exact, this is hardly true. 
That the reefs do curve somewhat is shown by the illustrations and 
maps given herewith. These curves, however, are always gentle, and it 
is only a matter of strict interpretation of language to say that they are 
not straight. 
Inasmuch as the reefs are only modified sand beaches, in order to 
understand their forms we must comprehend the forms of sea-beaches 
generally, and also to some extent the causes of such forms as we have 
along the Brazilian coast, 
Sand beaches, or beaches of construction, are built up with the mate- 
rials supplied by their own coast-lines : ent from headlands, washed down 
from the land by streams, or washed ashore by storm waves that throw 
them up from the shallow sea off-shore. The idea that has been put for- 
ward that the sands of the northeast coast of Brazil may have been 
brought from the west coast of Africa may safely be set aside as quite 
out of the question. 
Straight beaches may be produced in two ways : — 
I. By the elevation of a sea bottom, or the depression of a land sur- 
face that is so smooth that the new beach line, after elevation or depres- 
sion, is unbroken by surface irregularities. 
IL By the natural process of straightening an originally irregular, 
indented, or broken shore-line by the cutting down of the headlands and 
the choking up of embayments. 
In the latter case the beach is crooked at first and its straightness 
comes only with age. 
1 ГР Espace Celeste, p. 546. 
