168 BRANNER— THE FLUTING AND PITTING [April 4, 



in the Alps they hollow out enormous pot-holes In the rocks. The lake plain 

 is noted for the small amount of decomposition which has taken place over 

 it, owing, I believe, largely to the fact that it has never been covered by the 

 virgin forest, having always been dry." 



The explanation here suggested will be referred to later. 



Character of the Fluted and Pitted Rocks. 



The fluting of crystalline rocks is not confined to any one partic- 

 ular kind of rock, as was at first supposed, except that they are all 

 massive and homogeneous. Those about Quixada in Ceara vary 

 somewhat, but they are mostly massive coarse grained, gneissoid 

 granodiorites, and the weathered surfaces, though rounded in out- 

 line, are very rough, owing to the feldspar crystals standing out over 

 them in high relief. 



The rocks are often more or less jointed, and the joints neces- 

 sarily interfere with the regularity and extent of the fluting, though 

 they do not prevent it. Possibly abundant jointing may so interfere 

 with fltvting as to render it quite inconspicuous. 



The fluted rocks of the Itatiaya group are massive homogeneous, 

 coarse grained syenites, somewhat jointed, the joint planes having 

 various angles with the horizons, as may be seen in the accompany- 

 ing illustrations. The Itatiaya syenite is not as coarse grained, 

 however, as the granodiorite of Quixada. 



The fluting mentioned by Bauer in the Seychelle Islands is said 

 to be in granite. The examples seen by the writer in the state of 

 Pernambuco are all in granites. 



Origin of the Fluting. 



It was stipposed at the outset that chemical action over openly 

 exposed surfaces would turn out to be an important factor in the 

 production of the fluted forms. But it does not appear that such 

 action is especially important. It is evident that the rocks are 

 chemically afifected by the alteration of the feldspars, but there is no 

 apparent localization of that action in the case of the fluting. 



It seems most probable that in the long exposure of these homo- 



