On Spheroidal Jointing im Metamorphic Rocks. 343 
the observer meets with cases where the upper surface has been 
broken into, and the fact is then revealed that the domes consist of 
concentric shells, having a structure similar to that seen on the 
small scale, for example, in certain iron ores and in urinary 
calculi. (Plates 21 and 22.) 
As is represented, where the outer shell has been broken into by 
weathering or other causes, its fragments rest upon a smooth 
surface below. In some cases several successive shells are dis- 
closed, the planes of jointing separating ‘which, preserve a 
uniform distance from one another throughout, and cut through 
the crystals of felspar sharply, and at all angles as they follow 
the curves. 
The shells vary in thickness from about three to ten inches, 
but in any individual dome the thickness appears to be tolerably 
constant throughout each layer. If what has been above said is 
sufficiently clear, it will have been understood that the shells rest 
upon the surfaces of one another successively, like the shells of 
some nuts on their kernels. Supposing an outer shell to be 
removed, a perfectly smooth surface, which will soon receive a 
high polish from atmospheric agencies, is disclosed, and when in 
this condition the resemblance of the domes to veritable voches 
moutonnées is indeed striking. 
Now, what is the origin of this structure? It is unnecessary 
here to discuss the evidence for or against glacial actions having 
taken place in India, at a former period of the world’s history. 
Pretty complete evidence of floating ice having deposited its load 
of stones and mud in the Talchir (Permian ?) period is found in 
the peninsula ; but in the case at present before us, it is manifest 
that though a glacier is undoubtedly competent to chisel rocks 
into a dome-shaped contour, it does not possess the power of 
inducing a concentric shell structure in the mass of a rock. 
If other evidence were wanting, the conical shaped (Plate 23) 
hills, which are clearly due to a variety of the same structure, 
would dispose of the possibility of a glacial origin. 
Some local observers in India, struck with the phenomenon, 
have suggested that the splitting off of the successive shells 
might be due to sudden shrinkage, caused by showers of rain 
falling on the rock when highly heated by the sun; but I am 
not aware that this view has been adopted by anyone having a 
knowledge either of physics or geology sufficient to enable him 
