136 



REPORT- 



-1865. 



that of the fall of Meteorites upon it, by which its magnitude is augmented, 

 and that by the addition of materials homogeneous with those of its existing 

 elementary constitution, being chiefly "those chemical elements which are 

 present in the greatest quantity in the Earth's crust, and seem to be most 

 essential to its constitution. According to the principle of the adequacy of 

 Existing Causes, therefore, we must conclude that the fall of Meteorites is a 

 continuation or a residue of the process of formation of our planet, and that 

 the Earth was originally produced by the aggregation and coalescence of 

 Meteorites, or of greater masses into which they had previously coalesced. 



The " Theory of the Minor Planets " is briefly considered. All the pheno- 

 mena they present are regarded as supporting the conclusion that their pecu- 

 liar relations and community of character are not, as hitherto supposed, 

 effects of their having formerly constituted one heavenly body which has been 

 reduced to fragments, but of their being bodies intrinsically of the same 

 nature, meteoritic masses in fact, in an advanced intermediate state between 

 the condition of meteorites and that of true planets, in process of gradual 

 convergence towards each other, preparatory to their coalescence into one 

 greater planet. 



(6.) On the Microscopical Structure of Crystals. By H. C. Sorby, F.R.S. &c. 

 (Quart. Journ. Geol. Soc. vol. xiv. pp. 453-500). 



From the size of the vacuities seen by the aid of the microscope in certain 

 cavities contained in quartz, felspar, and other crystalline minerals, it is pos- 

 sible to calculate the circumstances of heat and pressure under which the 

 crystals were originally consolidated. On heating the crystals gradually, the 

 vacuous spaces gradually diminish and ultimately disappear. Their dimen- 

 sions in the natural state are therefore an exact measure of the contraction of 

 the incarcerated fluids in cooling down from the originally high temperature 

 of consolidation. Great liquid pressures at the time of consolidation tend to 

 diminish, and great temperatures to increase the size of the vacuous spaces 

 contained in the cavities in their ultimate or natural state. These fluid 

 cavities exist by millions in every specimen of ordinary quartz, and cause the 

 opacity of this (and the generality of other crystalline minerals) to the pas- 

 sage of the rays of light. Decrepitating crystals are familiar examples of 

 their occurrence among artificial products, such as those of salt, sulphate of 

 potash, nitre, &c. They are indeed of such universal occurrence in crystals, 

 as to form in mineralogy a microscopical test of crystalline aggregation. 



Fig. 2. 



By alternate overgrowths and restorations of the 

 crystalline figure in deposition, minute cavities are 

 constantly formed, especially when the deposition 

 is rapid (fig. 2). In these cavities a portion of the 

 flux, or mother-liquor, becomes incarcerated. The 

 foreign substance by which the deposition is for a 

 moment arrested so as to form the cavity is also 

 frequently caught up and confined within the 

 cavity. The cavities are irregular in size, but 

 generally take their figure from the crystalline 

 figure of the mineral. After being cooled down 

 from the temperature of deposition, the cavities 

 exhibit a variety of solid, fluid, and gaseous con- 

 tents, as well as a vacuity due to the total con- 

 traction of the incarcerated fluid. Various examples of cavities in the crystals 



