various parts of Scotland. 397 



by their accumulation become botryoidal, smaller spheres growing 

 out as it were from the larger ones. Detached specimens that have 

 been washed by the sea, exhibit the appearance of a bunch of 

 grapes, but in their native bed the intervals are filled with an ochry 

 clay. Their fracture shows the uniform aspect of siliceous schist, 

 being neither coated nor radiated ; and the rock agrees in every 

 respect, except its structure, with the bed of siliceous schist, which 

 is found not far off. 



I have only observed one other instance of a rock similar to this, 

 and it occurs also under amygdaloidaltrap at Talisker, in Sky.* I 

 have reason to suppose it of rare occurrence. In various parts of 

 the rocks which I have now described there are found natural joints, 

 which on being separated exhibit two smooth surfaces, absolutely 

 flat, and appearing as if they had been cut through by a sharp tool. 

 The globular bodies themselves are divided in various parts, just as 

 they happened to interfere with the section. In the greater number 

 of the sections which I examined, no substance was interposed be- 

 tween the touching faces. But in some I found wavellite, a mineral 

 as yet not so common, but that this new habitat will be acceptable to 

 the mineralogist. It is remarkable that the circles of wavellite oc- 

 cupy precisely the surface of each segment of the several spheres, 

 varying in size according to the varying dimensions of these seg- 

 ments. This bed is covered by one of trap, or to use the term in 

 its present great latitude, of greenstone, forming a parallel bed of a 

 more considerable thickness, but with the same inclination as the 

 subjacent strata. This bed of greenstone weathers so as to exhibit 

 distinct globular concretions, although in its entire state the eye can 



* I have since observed a similar modification in the schist of Devonshire in which 

 wavellite is found. 



