64 My Hatch, Note on a Remarkable Instance, etc. 
originally cemented the constituent quartz grains of these pebbles 
has been wholly abstracted, leaving the quartz particles as a 
friable, almost non-coherent mass, easily reducible to powder 
between the fingers. In other cases the pebbles consist of 
tourmaline and quartz, and were evidently derived from pre-— 
existing veins. These also have been reduced by the same 
weathering action to a loose friable condition. It is clear that 
the fragments of both these materials could only have acquired 
their rounded character by water-attrition when they were in a 
hard, compact and firmly-knit condition. Evidence is thus 
afforded both of the profound nature, and the prolonged duration 
of the weathering to which the conglomerate must have been 
exposed since its first formation*. 
* Compare: J. G. Branner, The Decomposition of Rocks in Brazil, Bull. Geol. 
Soc. Amer. Vol. vit. 1896, pp. 295—300. 
