in the Neighbourhood of Edinburgh. 41 



from which these rocks will be found to decline in opposite di- 

 rections. 



The researches of several eminent philosophers relative to the 

 interior temperature of the earth, have given rise to the hypo- 

 thesis now very generally received, which refers the extensive 

 changes of level between the sea and land, that have taken 

 place in all ages, and may probably be going on, although in a 

 less sensible degree, at the present moment, to the effect pro- 

 duced on its surface by the secular refrigeration of the globe, 

 and its inequality in cooling. At so early a period in the history 

 of our planet, as that which we are now considering, the heat be- 

 ing much greater, the process of refrigeration, and the consequent 

 contraction of the crust of the earth, must have been more 

 rapid, and the production of gases, from the superficial consoli- 

 dation of the interior fluid, more abundant. The force, there- 

 fore, which in our days is seen to cause volcanic action, would 

 then have been exerted with greater intensity, so as to have oc- 

 casioned not only the ejection of a much larger quantity of the 

 igneous matter to the surface, but also elevations of land, on a 

 much more extensive scale than we can form any idea of, from 

 the greatest effects of the most active volcanoes in modern times. 



The rock upon which the Castle is situated, consists of green- 

 stone of a hard and compact nature, and of a dark grey colour, 

 approaching to black. It is throughout of the laminar structure, 

 which, in several places, gives it a false appearance of stratifica- 

 tion. Some of the lamina may be seen passing into the cuboidal 

 or square prismatic structure, and occasionally to split into im- 

 perfectly columnar divisions. Within the Castle walls fragments 

 of sandstone are imbedded in the trap, and near its south-west 

 point, altered rocks, apparently of sandstone and slate-clay, are 

 observed resting upon it in a highly inclined position. 



The situation of the section of the Castle Hill, lately made in 

 cutting the new South-west Road, and the relative position of 

 the stratified rocks displayed in it, will be better understood by 

 a reference to the accompanying drawing, which has been very 



VOL. XIII. PART I. F 



