While recognizing the importance of Philpotts' ( 1968) experimental model in demonstrating thermal convection in two immiscible liquids in a vertical tube, the validity of the application of the experiments and their results to the origin and mechanism of emplacement of Mount Johnson is questioned. Some of the structural and petrological interpretations presented by Philpotts are questionable and do not necessarily indicate that the origin of vertically layered rocks in Mount Johnson is due to thermal convection in a body of magma solidified from the wall inward. Structural, petrographic, and mineralogical evidence studied by the present authors along two sections (one on the SW and the other on the NE) of Mount Johnson (Bhattacharji 1966; Bhattacharji and Nehru, in preparation) do not support Philpotts' model but suggest the intrusion of an early, partly crystallized (solid with immobilized interstitial fluid) essexite core into a partly differentiated fluid which crystallized to a rock of pulaskitic composition. Crystallization and magmatic differentiation in the magma chamber and/or in the conduit before and during intrusion (bodily movement) coupled with the concentration of volatiles along the sheared boundary between mostly solid essexite and mostly liquid marginal pulaskite and flow differentiation en route in the niarginal fluid concur better with the available data on Mount Johnson. The details of our evidence and experimental model studies will be published elsewhere and only a short discussion of our work relevant to Philpotts' ideas and model experiments is presented here. While Philpotts states that the intrusion consists of four main rock types (pp. 1 13 1-1 132) and that all rock types of the intrusion are strongly foliated, our systematic study of two sections of this intrusion confirms Adams' (1903) contention of three zones namely, (1 ) inner essexite zone, (2) middle transitional zone more closely related to the essexite, and ( 3 ) the outer pulaskite zone. As opposed to Philpotts' idea of distinct "olivine-essexite" core of 210 m in the central part of the intrusion, our studies (of about thirty modes from the two sections) indicate that olivine is rather irregularly distributed throughout the essexite and transitional zones. In some parts of the sections (particularly NE side) olivine is essentially absent. The rock in the central area of the essexite core (Philpotts' "olivine essexite zone") is not strongly foliated as described by Philpotts. Philpotts' main contention against fractional crystallization, that the rock of the "core resembles a chilled contact" and that the olivine is a late crystallized mineral from the interstitial liquid between the feldspar laths, is untenable. His own description "the core . . . . . is fineto medium-grained" (p. 1132) and our petrographic studies do not show any evidence for the central essexite core resembling a chilled contact. In all the thin sections examined by us, the olivine often shows resorption phenomena (Plate I ) and definitely appears to be an early crystallized phase. Philpotts (pp. 1133-1 134) suggests that in Mount Johnson the solidification in a convecting body of magma was preceded by accumulation of minerals on the walls of the magma chamber (conduit?). In such a convecting body of magma the crystals which grow along the margins will either be attached to the walls or be carried into the magma reservoir. Philpotts envisions that the downward convection currents along the walls were so strong that they could downwarp the surrounding country rock