Intelligence and Miscellaneous Articles. 441 



It has recently been proposed to regard the felstone of this district 

 as a lava-flow of Mid-Cambrian age, and the beds to the north as 

 lower strata included in the same great series. The author points 

 out as objections to this view: — (1) the enormous thickness of beds, 

 which in that case must be cut out by the supposed Arenig uncon- 

 formity at Caernarvon ; (2) the difficulty of assigning two felsite 

 masses lithologically similar to two distinct periods ; and (3) the 

 occurrence of conglomerates similar to those which are elsewhere 

 admitted to be basal Cambrian. But in addition to these minor 

 difficulties, the theory of a Mid-Cambrian age for the above-named 

 lava is shown to be without foundation. It was supposed that in the 

 Bryn Efail quarry the slaty rocks of the district immediately to the 

 north could be seen in contact with, and altered by, this lava. The 

 author shows that no slate occurs in the quarry, a diabase having 

 apparently been mistaken for it, and that there is no grit in the 

 section which would afford any support to the new theory. The 

 author concludes that the Llyn Padarn felsite is probably, as 

 classed by Dr. Hicks and Prof. Bonney, of pre-Cambrian age. As 

 regards the country to the north, the argument for the arrange- 

 ment was based mainly on the interpretation of the Bryn Efail 

 rocks ; but as this is seen to be erroneous, the section founded on it 

 does not appear preferable in any way to that published by the 

 Geological Survey. 



LVL Intelligence and Miscellaneous Articles. 



SOME KEMAEKS ON THE KINETIC THEORY OF GASES. 

 BY S. TOLVER PRESTON. 



rpHE theorem that the velocities of the molecules of a gas vary 

 -*- "between zero and infinity" (between zero and a velocity 

 indefinitely great) would seem to give the idea that the velocities are 

 enormously great sometimes. 



But it would appear that there are distinct physical conditions 

 tending to limit the velocities of the molecules of a gas (i. e. the 

 velocities capable of being acquired in the accidents of collision). 

 Eirst, there is the friction of the molecules in their passage through 

 the aether. This must be considerable at high velocities, since 

 meteoric dust is measurably retarded from this cause ; and the 

 relative friction or resistance to passage increases as the size of the 

 body diminishes. So that probably by the known small size of 

 molecules, the friction must be very great. Second, the resistance 

 to passage is augmented from the fact that the molecule is in 

 vibration (or some analogous motion about its centre of gravity) 

 in the aether. The molecule is like a rough body then, stirring up 

 the aether during its translatory motion, which must greatly 

 augment the resistance to passage. That there is friction in the 

 aether by the passage of molecules is also confirmed, as it seems, by 

 the fact that waves of heat and light contain energy. Eor how 



