194 Proceedings of the Royal Society of' Edinburgh. 



made in cutting the new south-west road has displayed appearances, 

 which, in the author's opinion, supply strong evidence that, subse- 

 quent to such eruption, the secondary and trap-rocks had been up- 

 lifted together by a common cause, probably acting on a great extent 

 of the face of the country. This section shews five or six beds of 

 sandstone, with alternate layers of slate clay or marl. Signs of 

 great confusion are found in these strata, more especially as they 

 approach the point of junction with the trap-rock, — their eastern ex- 

 tremity being thrown upwards, while their western portion is cast 

 down, so as to lie unconformably on the upturned strata ; and near 

 the point of junction with the greenstone, the ends of the strata of 

 sandstone and slate-clay are shattered, and have actually fallen over, 

 so as to come obliquely in contact with the tabular masses of the 

 greenstone. Yet it is remarkable, that the sandstone and shale pre- 

 sent no appearance of semi-fusion or intermixture, where they are 

 in contact with the greenstone ; nor does the greenstone here pre- 

 sent any imbedded masses of the secondary rocks, nor send out any 

 veins among their adjacent strata. At the time, therefore, when 

 the dislocation of the sandstone strata occurred at the point of junc- 

 tion with the greenstone, the latter could not have been in a state of 

 fusion 5 and the only rational explanation which occurs is, that both 

 rocks were raised, in a solid state, by some common cause, above the 

 level of the waters under which they were originally formed ; and 

 that the fault or dislocation in the sandstone strata was produced by 

 some subsidiary disturbing power acting at the same period. 



2. Researches on the Vibrations of Pendulums in Fluid Me- 

 diums. By George Green, Esq. Communicated by Sir 

 G. Ffrench Bromhead, Bart. 



The author proposes in this paper to resolve a particular case of 

 the motion of fluids, not previously noticed, and susceptible of prac- 

 tical application, namely, the circumstances of the motion of an inde- 

 finitely extended non-elastic fluid, where agitated by a solid ellipsoi- 

 dal body moving parallel to itself, according to any given law ; always 

 supposing the body's excursions very small compared with its dimen- 

 sions. The question here stated is considered by the author to ad- 

 mit of an easy general solution. As the principal object of his paper 

 is to determine the alteration produced in the motion of a pendulum 

 by the action of the surrounding medium, he insists more particu- 

 larly on the case where the ellipsoid moves in a right line parallel to 

 one of its axis ; and endeavours to prove that, in order to obtain the 

 correct time of a pendulum's vibration, it will not be sufficient merely 

 to allow for the loss of weight caused by the fluid medium, but that 

 it will likewise be requisite to conceive the density of the body aug- 

 mented by a quantity proportional to the density of this fluid. He 

 determines the value of the quantity last mentioned, when the body 

 of the pendulum is an oblate spheroid, vibrating in its equatorial 

 plane; and finds, that when the spheroid becomes a sphere, the 

 quantity is precisely equal to half the density of the surrounding 

 medium. Hence in the last case, the true time of the pendulum's 



