52 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
there it is as flat and smooth as any sandstone slab for hundreds of 
metres; again it is so rough and uneven that it is almost impossible to 
walk over it. Over much of the surface there are shallow depressions 
that look like gigantic footprints made by mud-clogged feet in thick 
mud. At such places the surface of the reef has a profile like this : 
IN 
Fig. 22. Section across the Mamanguape stone reef. 
In plan these pits have these and similar forms (Fig. 23) : 
These pits are from three to seven 
centimetres deep and from a few centi- 
М ar . М 
C metres to two metres long. or the 
D (/ D | most part they are parallel, but some- 
» 0 D times they stand at various angles to 
DS () each other. 
The Mamanguape reef has some fine 
examples of etched surfaces. One of 
Fie. 23. Forms of the pits on | : 
surfaceof the Mamanguapereef. these is shown in Plate 41, a photo- 
graph taken near the inner edge of the 
reef on its southern half. This etching leaves ragged sharp points that 
vary in height from a few centimetres to a metre, and a great number of 
fantastic forms. 
Fig. 24. Characteristic forms produced by the etching of the Mamanguape 
stone reef. 
Some of the pillars on the Mamanguape reef are as much as two 
metres high; the tall ones are, as a rule, on the landward side of the 
reef, — never close to Ше surf-beaten sea side. These spike-like projec- 
