Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 37 



33. From our assumptions respecting the variable cohesive power 

 of the mass, it is manifest that different fissures might commence simul- 

 taneously at different points, and be propagated in opposite directions. 



Thus, suppose the fissure CB to commence at D, when AB and £'/^ com- 

 mence at A and E re.spectively. When the first of these arrives at C, 

 as the two others arrive respectively at B and F, the further propagation 

 of each of them may be prevented by the relaxation of the mass. Con- 

 sequently a system of fissures might thus be formed similar to that 

 represented in the above figure. 



§. Application of the previous Propositions to a Mass of three dimensions. 



34. These investigations have been applied immediately to the case 

 of a thin lamina, to avoid the complexity which would necessarily have 

 been introduced in their immediate application to a mass of three di- 

 mensions. The extension of the preceding propositions, however, to this 

 latter case is sufficiently obvious to require little more than an enun- 

 ciation of the results, which may also serve as a summary of the 

 most important of those at which we have arrived in this section. 



A slight inspection of what has been advanced in Art. 1.5, will 

 shew that the existence of a line of less resistance in a thin lamina, 

 will have no effect on the propagation of a fissure hi a direction per- 

 pendicular to it; and similarly, if we suppose any mass acted on by 

 horizontal tensions, it is manifest that a horizontal plane of less resist- 

 ance will have no effect on the verticality or horizontal direction of 

 the vertical fissures resulting from such tensions. Consequently, tlie 

 tensions being horizontal, the cohesive power of the mass may be' sup- 



