280 
APPENDIX. 
This is a fine example of what apparently inefficient means 
may be effectual. 1 
I believe that similar bars of rock occur in front of some 
of the other bays and rivers on the coast of Brazil : Baron 
Eoussin states that at Porto Seguro there is a ‘ quay ’ simi- 
lar to that of Pernambuco. Spaces of several hundred 
miles in length on the shores of the Gulf of Mexico, the 
United States, and of Southern Brazil are formed by long 
narrow islands and spits of sand, including extensive shal- 
low lagoons, some of which are several leagues in width. 
The origin of these linear islets is rather obscure : Pro- 
fessor Rogers (Report to British Association, vol. iii. p. 13) 
gives reasons for suspecting that they have been formed by 
the upheaval of sand-hanks, deposited where currents 
formerly met. The bar of sandstone at Pernambuco has 
probably been formed in an analogous manner. The town 
stands partly on a low narrow islet and partly on a long 
spit of sand, in front of a low shore, hounded in the distance 
by a semicircle of hills. By digging at low water near the 
town, the sand is found consolidated into sandstone, similar 
to that of the bar, but containing many more shells. If, 
then, the nucleus of a spit of sand, extending in front of 
the hay, had formerly become consolidated, a small change, 
probably of level, hut perhaps merely in the currents, might 
have given rise, by washing away the loose sand, to a struc- 
ture like that of the bar in front of Pernambuco and along 
the coast southward of it ; but without the protection af- 
forded by the successive growth of the above-named organic 
beings, its duration would have been short. 
1 [There is an interesting account of this reef, containing particulars 
of some borings undertaken in 1874, by Mr. J. C. Hawkshaw, in the 
Quarterly Journal of the Geological Society for 1879 (vol. xxxv. p. 239).] 
