PART 4.] 
Theobald: Remarks on Mr, Wynne’s paper, fyc. 
223 
Another curious class of crystals has been observed. At first sight they would seem to 
be illustrations of what Sorby calls stone cavities ; that is to say, one mineral held in solution 
by another in a state of fusion and deposited on cooling. But as the dark opaque mineral is 
sometimes seen uninclosed by crystals and at other times is attached externally to crystals, I 
conclude that the dark minerals were first formed and the crystals were afterwards formed 
around them, or they were both floating about in a plastic state in the matrix and the dark 
minerals were absorbed into the white ones. I infer that the dark mineral was in a plastic 
state when the white mineral formed around it, or absorbed it into its own body, from the 
fact that where the dark mineral touches the outer sides of the white, crystals, its surface 
generally conforms to the outline of the containing crystal as closely as if it had been deposited 
from a solution within the crystal itself. In one case when one of the dark minerals is seen 
riding astride on the back of a white crystal, it was observed that it had embraced the 
rounded form of the latter. 
The study of the belonites contained in the felspar of the granitoid gneiss satisfies me 
that the central gneiss in its granitoid form was reduced to a plastic condition. Some of 
these belonites are very long, and occupy, in length, three or four fields of the microscope. 
Examples of belonites fractured and thrown out of their orignial position are not uncommon. 
Some can be distinctly traced to the physical strain of one belonite on another. These are 
not cases of irregularities of growth, but of distinct fracture after the formation of the 
belonites. A very striking instance (a most convincing one when actually seen under the 
microscope) occurs in which one of the fractured pieces is turned nearly at right angles to its 
original direction. The matrix must have been in a perfectly plastic condition to have 
allowed of this movement and to have flowed in round the fractured ends so as to leave no 
trace of the disturbance. I cannot believe that these fractures were simulated at the original 
formation of these crystals. I would as soon hold that the dip and contortion of strata are 
due to peculiarities in the original deposition of the beds. 
The facts detailed in these observations show, I think, that the central gneiss has been 
subjected to great heat, and that where it passed into a granitoid condition, it became perfectly 
plastic. 
In view of these results I think it would require strong evidence to justify the belief that 
the unaltered rocks of the Ivrol and Infra-Urol series underlie the crystalline rocks of the 
Central Himalayas. 
The glass cavities, belonites, &c., described in these rocks, were seen under a magnifying 
power of 4-50 diameters. 
Remakes, explanatory and ckitical, on some statements in Me. Wynne’s papek on 
the Tektiabies of the Nouth-West Panjab in Records, Vol. X, Pakt 3, BV 
W. Theobald, Geological Survey of India. 
In Mr. Wynnes interesting sketch of the tertiary rocks of the North-West Panjab, 
there are a few points whereon I should like to make some remarks in correction, as I believe, 
of some of the views adopted. 
Under the head “ Erratics ” (page 123 l. c.), Mr. Wynne enumerates numerous examples, 
regarding whose origin and character there can he little doubt, save with those who altogether 
decline to recognise the existence of glacial conditions in Northern India during recent times; 
hut, in addition to these, my colleague describes others, which are not only, in my opinion, not 
‘ erratics ’ at all, but belong to diverse geological epochs. 
