Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 49 



extremities of those lines at C will separate from each other by the con- 

 traction of AC and MC ; and the same will be true for every similar pair 

 of lines. An extension of the orifice at C will thus be produced, and con- 

 sequently a tension of the mass contiguous to it in the direction of a tangent 

 to a horizontal section of it, while tiie tension in the direction of such 

 lines as C'A' will be entirely destroyed near to C, and much lessened 

 at lower points. The whole tension therefore in the upper part of the 

 mass, will be in the directions of the tangents of horizontal circles con- 

 centric about the axis ; and the tendency to form a fissure there, will 

 be entirely in a vertical plane passing through the axis of the cone. 

 It is easily seen also that the tension at the vertex will be greater 

 than in any other part. Consequently, if fissures be formed under 

 these circumstances, they will commence at the vertex, and be in posi- 

 tions such as that just mentioned. 



48. Let us now suppose the elevatory force to act with additional 

 intensity beneath the point C of the annexed diagram, (which repre- 

 sents a horizontal section,) so as to superimpose on the general elevation 



a conical one, having its apex at C. In addition to the tension {F) 

 acting at any point P within the bounds of the cone, and in the 

 direction perpendicular to the general axis of elevation, we shall also 

 have another tension (/) acting at P, in the direction PQ' perpen- 

 dicular to CP, (taking the case of Art. 47.) and the tendency of these 

 tensions will be to form a fissure deviating from perpendicularity with 

 PQ, in a degree depending on the relative intensities of f and F. 

 Consequently, a fissure A'PB' will deviate from parallelism with the 

 line of general elevation, approximating towards C in the manner above 

 represented. 



49. If the partial elevation instead of approximating to tiie conical 

 form, be more nearly spherical, without any such rupture at C, as 

 Vol. VI. Part I. G 



