In the Abstract of his paper on the "Evidence of Assimilation and Assimilation Processes" Mr. Bain states that he is here dealing with the general process of assimilation. His paper itself, however, treats in considerable detail of the Sudbury "norite-micropegmatite." Nowhere does he bring forward any satisfactory evidence for linking up these two subjects. The only feature of the whole Sudbury region to which he can point as giving him occasion to consider assimilation in this specific instance is "the mysterious absence" of sediments on one side of the igneous outcrop which occur on the other. Arguing on this basis we should consider that assimilation has been operative in the case of all dykes which have been intruded along a fault plane. In the case of the rocks at Sudbury, Knight' has already suggested that the whole Sudbury "basin" represents a down-faulted block. If this is true, the rocks met in the interior of the "Nickel Ranges" must be younger than those on the periphery. Again, Coleman2 holds that the locus of the "norite-micropegmatite" intrusion has been a plane of unconformity, so that there could be no congruence between the material within and without the igneous outcrop. Whether these explanations are correct or not remains for more detailed field work to decide, but, in any case, either theory is to be preferred to an explanation based on assimilation of which absolutely no evidence is to be found in the rocks concerned. In his treatment of this matter of assimilation Mr. Bain has adopted a most abstract method of approach. Neither assimilation nor any other theory of petrogenesis has its basis in physical chemistry, although it must conform to the laws of that science. It is fu-