Discussion

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Abstract
Dr. H. I. D rever said that the author had kindly shown him his specimens and given access to his recorded results. The speaker had also examined this remarkable and important intrusion for about two hours last summer in the company of Mr. R. Johnston. Its two most significant characteristics seemed to be the evenness of the lower bands and the concentration of a feldspathic facies almost, if not actually, at the upper margin. These two phenomena had no near counterpart in any ultrabasic sill previously recorded. The author’s investigation was amply justified, and the speaker considered that a further, and even more detailed, investigation would be justified and rewarding. Exceptional petrological problems such as this one were most likely to yield observational data of critical and fundamental significance. Such exceptions would improve the rule by revealing its limitations or by defining its limits more accurately. The rule in the present instance was the well-established petrological principle of crystal settling. The author had invoked this principle in an explanation that demanded a dominantly upward consolidation of the sill. In such a small sill, visibly connected with a feeder dyke below, it would be expected that consolidation of the feldspathic peridotite would be relatively more rapid in a downward than in an upward direction. If this were true, another explanation must be sought for the concentration of pegmatitic material so near to the top. The speaker was familiar with the micropetrography of pegmatitic bands similar to those described in the paper, and

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