ZOOLOGY. 211 



Fourier's theory of the conduction of heat to trace the earth's thermal 

 history backwards. From data regarding the specific heat and thermal 

 conductivity of the earth's substance, he investigates the time that must 

 elapse from an epoch of any given uniform high temperature through- 

 out the interior, until the present condition of underground tempera- 

 ture could be reached. Taking into account the very uncertain char- 

 acter of the data when high temperatures are concerned, he infers that 

 most probably either the whole earth must have been incandescent at 

 some time from 50,000,000 to 500,000,000 years ago, or that at some 

 less ancient date, but still anterior to the earliest human history, there 

 must have been up to the surface a temperature above the boiling 

 point of water. Either alternative or indeed any theory whatever 

 consistent with the principles of natural philosophy regarding previous 

 conditions of the earth is as decisive against the views of those nat- 

 uralists who acknowledge no creation of life on the earth within fath- 

 omable periods of time, as the plainest elements of dynamics are against 

 those who maintain that we have no evidence in nature of an end." 

 Edinburgh New Philosophical Journal. 



THE FORMS OF STRATIFIED ROCKS. 



The following is a report of a lecture, embodying some curious and 

 original views, delivered before the Royal Institution, London, by Mr. 

 J. Ruskin, the well-known writer on art. The purpose of the dis- 

 course was to trace some of the influences which have produced the 

 present external forms of the stratified mountains of Savoy, and the 

 probable extent and results of the future operation of such influences. 

 The subject was arranged under three heads, 1. The Materials of the 

 Savoy Alps. 2. The Mode of their Formation. 3. The Mode of their 

 subsequent Sculpture. 1. Their Materials. The investigation was 

 limited to those Alps which consist, in whole or in part, either of Jura 

 limestone, of Neoeomian beds, or of the Hippurite limestone, and in- 

 clude no important masses of other formations. All these rocks are 

 marine deposits ; and the first question to be considered, with respect 

 to the development of mountains out of them is the kind of change 

 they must undergo in being dried. Whether prolonged through vast 

 periods of time, or hastened by heat and pressure, the drying and solid- 

 ification of such rocks involved their contraction, and usually, in con- 

 sequence, their being traversed throughout by minute fissures. Under 

 certain conditions of pressure, these fissures take the aspect of slaty 

 cleavage ; under others, they become irregular cracks, dividing all 

 the substance of the stone. If these are not filled, the rook would be- 

 come a mere heap of debris, and be incapable of establishing itself in 

 any bold form. This is provided against by a metamorphic action, 

 which either arranges the particles of the rock, throughout, in new 

 and more crystalline conditions, or else causes some of them to separate 

 from the rest, to traverse the body of the rock, and arrange themselves 

 in its fissures ; thus forming a cement, usually of finer and purer sub- 

 stance than the rest of the stone. In either case, the action tends con- 

 tinually to the purification and segregation of the elements of the stone. 

 The energy of such action depends on accidental circumstances. First, 

 on the attractions of the component elements among themselves ; sec- 

 ondly, on every change of external temperature and relation. So that 



