162 Notices of Memoirs — D. Forbes, F.E.8., 



partly by tidal action, in the bottom of one of tlie old north and 

 south longitudinal valleys, mentioned as occurring so frequently in 

 Cheshire ; on the emergence of the country it was re-excavated by 

 the Mersey, which cut for itself a fresh channel in the Drift, in 

 addition to excavating out the Wallasey Gorge, and cutting its pre- 

 sent course between Egremont and Liverpool, which is daily becom- 

 ing wider and wider, under the horizontal denuding power of tidal 

 waters. 



nsroTiciBS OIF DvniEivaioiie'S- 



On the Nature of the Earth's Interior.^ 

 By David Forbes, F.E.S., etc. 



IN a previous discourse on Volcanos, Geological Magazine, 

 1870, Vol. YII., p. 314, attention was directed to the phenomena 

 of volcanic action, specially considered in relation to the part which 

 such igneous or internal forces have played in determining the grand 

 features of the external configuration of the sphere upon which we live. 



If, now, we follow up this subject still further, it will naturally 

 lead to an inquiry into the nature of the internal substance of the 

 globe itself, within which the foci of such agencies must be situated; 

 but quite independent of this, there can be little doubt but that 

 most intelligent persons have at some time or other already asked 

 themselves the question as to what the central mass of the earth 

 beneath them consisted of. 



The answer which in the first instance would be most likely to 

 suggest itself to the mind would be, that it consisted of solid stony 

 matter, such as is seen forming the body of its mountains, the foun- 

 dation of its continents, and the rock basins which contain its seas. 

 The belief in such an hypothesis would, however, be rudely shaken 

 by the first personal experience of the shock of an earthquake, the 

 sight of a volcano in eruption, or the consideration of the immense 

 faults which, in many places have disturbed and dislocated the solid 

 land ; whilst, so far from disposing us to regard the ground under 

 us as entitled to the appellation of terra Jinna commonly employed 

 by the ancients, the study of such phenomena could not but suggest 

 grave doubts in our minds as to whether the earth, after all, could 

 be anything like so solid and stable as at first sight we might have 

 felt inclined to suppose it. 



But very little inquiry into this subject is necessary, however, to 

 convince any one of the great difficulties in the way of obtaining a 

 satisfactory answer to this question, and to prove that in the present 

 state of science we have not at our command sufficient data or 

 evidence to enable us to arrive at any thoroughly conclusive solution 

 of this most interesting problem. 



As the rapid advances made by the natural sciences in all 

 directions are, however, daily adding to our information bearing 

 upon this subject, and thereby enabling previous deductions to be 



1 A lecture delivered ia St. George's Hall, January 29, 1871. 



