branner: the stOxNE reefs of brazil. 51 



which are larger than one's fist. Mingled with the quartz are also, both 

 here and elsewhere over the reef's surface, large pebbles of dark red 

 Cretaceous or Tertiary sandstone such as occurs in the hills that skirt 

 this coast. There are also occasional patches and lumps of a very black, 

 compact, heavy rock made up of grains of titaniferous iron. At one place 

 near Mamanguape Point a piece of this black iron rock, 4' X 4' X 5", was 

 found on top of the reef cemented compactly to an underlying bed or 

 coarse white sand and pebbles. This rock is as black as coal, is com- 

 posed of particles of black titaniferous iron sand, and shows false bed- 

 ding. A few other blocks of similar material, one foot square, are near 

 this one and attached in a similar fashion. Half a mile further south 

 angular and subangular fragments of this rock the size of the two fists 

 and some as big as one's head ai'e buried in the sugar-brown rock of the 

 reef, forming a sort of breccia for fifteen metres or more. At many other 

 places this material occurs as pebbles scattered through the brown reef 

 rock. These spots are caused by the concentration of titaniferous iron 

 sands upon the ancient beaches. They ai-e cemented by carbonate of 

 lime and magnesia in the same manner as the other reef rock. 



The most characteristic thing about the rock of this and of all the 

 other stone reefs is the presence in them of fossil shells of various mol- 

 lusks now living along the coast. These shells are not evenly distributed 

 through the rock, but are abundant in some layers and almost or quite 

 wanting in others. Most abundant of all is a small, beautifully varie- 

 gated, thick-shelled Venus known here as mariscos. These shells still 

 retain in the rock their brilliant colors. The shells are never found in 

 pairs as in life, but broken apart and with the horny cuticle they have 

 when alive worn off. Daring their lives these mcwucos burrow in the 

 sand of sandbars and protected sandy beaches to a depth of about two 

 inches. Thev are edible, and are used for food more or less all along 

 the coast. 



In one of the blocks near the northern fourth of this reef was found 

 also a block of Porifes, one of the hardy corals now growing upon the 

 coral reefs and in the rocky tide-pools of the coast. 



The reef rock proper when found in large slabs or projecting points 

 rings under the hammer almost like bell-metal. It is, however, not 

 everywhere equally hard : the upper beds, especially those exposed now 

 and then to the sun and atmosphere, are as a rule hard and even 

 quartzitic in fracture, while in other places the same beds may be 

 rather soft and incoherent. 



The surface features of the reef are not without interest. Here and 



