246 Dr. J. A. Smythe — Inclusions in 



and this observation has heen confirmed by the experience gained in 

 grinding the thin sections. In the fresh rocks there is no plane of 

 weakness between the unfacetted portion of an inclusion and the 

 surrounding normal whin, so that the spherical shape of the former 

 is not displayed. 



Another curious observation is deserving of mention. When the 

 field-work was about half completed the general impression had been 

 gained that the moulds of the inclusions, exposed by the breaking of 

 the whin, faced upwards. Special attention was afterwards paid to 

 this point and the impression was completely confirmed. 



Thus one may say with considerable probability that the inclusions, 

 spherical in a general way, are, in their natural position, only facetted 

 on the lower hemisphere. 



Detailed Description of the Liclusions. 



Observations made on the collected material will now be considered 

 in detail, and attention "will be directed to some characteristics of the 

 inclusions as defined by the facets. The normal aspect of these is 

 that of a hemisphere round which the facets are arranged tangentially. 

 Deviations from this type are, however, not uncommon. In a few 

 cases two inclusions are joined by a narrow facetted ridge. Some 

 individuals are collapsed in the middle ; less frequently they appear 

 crushed and flattened, the facets being irregularly, though locally, 

 dispersed through the rock, and a few specimens show one inclusion 

 within another. 



The facets vary in number and size without regularity, some 

 specimens having as many as fifty. These are often circular, or rudely 

 so, and the contact is imperfect, non-reflecting basalt occupying the 

 spaces and coigns between tliem (PL XVII, Fig. 1). At times 

 the shape is rudely pentagonal or hexagonal, or irregularly 

 polygonal, and in these cases the junction of contiguous facets is 

 frequently a perfectly straight line. 



The most striking character of the facets, however, is their 

 crystalline structure, occasionally visible with a hand-lens, but 

 usually requiring observation through a microscope. This phase of 

 the subject has been studied in some detail, and many of the most 

 pronounced features have been photographed in reflected light, using 

 both oblique and vertical illumination. For photographic purposes 

 oblique illumination is somewhat unsatisfactory, as it is almost 

 impossible to use high powers and to get much of the field in focus. 

 These difficulties do not beset the operations when vertical illumina- 

 tion is employed. Nevertheless, for purposes of observation only, 

 the former method is greatly to be preferred. 



For convenience of description the observations will be classified 

 as appertaining to the clear, glassy-looking surfaces of the knohs and 

 moulds^ (white, blue, or slightly bronze in colour, according to the 

 incidence of the light) and the ihinfilm of pronounced bronze colour 

 which separates these surfaces. 



^ The term ' mould ' is used in this connexion without any implication that 

 the knob has taken its shape from the mould. The observations, in fact, 

 rather point to the contrary. 



