298 ANNUAL OF SCIENTIFIC DISCOVERY. 



law of density of the nucleus will not be the same as that of the primitive 

 fluid, but will vary more slowly, and the mass will thus tend towards a state 

 of homogeneity as the radius of the nucleus diminishes by the gradual thick- 

 ening of the shell. The surface of the nucleus, and consequently the inner 

 surface of the shell, will thus ten-i to tecoiuo nnre oblate after each successive 

 stratum added to the shell by congelation from the nucleus. This result, 

 combined with another obtained by Mr. Hopkins, proves that so great pres- 

 sure and friction exist at the surface of contact of the shell and nucleus as to 

 cause both to rotate together nearly as one solid mass. Other grounds for 

 believing in the existence of the great pressure exercised by the nucleus at 

 the surface of the shell were adduced. If the density of the fluid strata were 

 due to the pressures they support, and if the earth solidified without any 

 change of state in the solidifying fluid, the pressure against the inner surface 

 of the shell would be that due to the density of the surface stratum of the 

 nucleus, and would, therefore, rapidly increase with the thickness of the shell. 

 Contraction in volume of the fluid on entering the solid state would diminish 

 this pressure, but yet it may continue to be very considerable, as the co-effi- 

 cient of contraction would always approach towards unity. The phenomena 

 of the solidification of lava and of volcanic bombs were referred to hi illus- 

 tration of these views, and their application was then shown to some of the 

 greatest questions of geology. The relations of symmetry which the researches 

 of M. Elie de Beaumont seem to establish between the great lines of elevation 

 which traverse the surface of the earth appear to Prof. Hennessy far more 

 simply and satisfactorily explained by the expansive tendency of the nucleus 

 which produces the great pressure against the shell than by the collapse and 

 subsidences of the latter. The direction of the forces which would tend to 

 produce a rupture from the purely elevatory action of the pressure referred to 

 would be far more favorable to symmetry than if the shell were undergoing a 

 distortion of shape from collapsing inwards. The nearly spherical shape of the 

 shell would also greatly increase its resistance to forces acting perpendicularly 

 to its surface, so as to cause it to subside, while the action of elevatory forces 

 would not be resisted in the same manner. 



ON THE OCCURRENCE OF NUMEROUS FRAGMENTS OF FIR AVOOD IN 

 THE ISLANDS OF THE ARCTIC ARCHIPELAGO. 



From a recent communication made by Sir R. I. Murchison to the Lon- 

 don Geological Society, on the above topic, we derive the following ab- 

 stract: 



My chief object, said Mr. M., is to call attention to the remarkable fact of 

 the occurrence of considerable quantities of wood, capable of being used for 

 fuel or other purposes, which exist in the interior and on the high grounds of 

 large islands in latitudes where the dwarf willow is now the only living 

 shrub. 



Before I allude to this phenomenon, as brought to rny notice by Capt. 

 M'Clure and Lieut. Pirn, I would, however, briefly advert to a few rock speci- 

 mens collected by the latter officer in Beechey Island, Bathurst Land, Eglin- 

 ton Island, Melville Island, Prince Patrick's Island, and Banks' Land. 



