40 



Mr. Hopkins on the Structure of the 



that we cannot possibly know sufficiently the exact conditions of the problem to 

 determine the precise position of each individual fissure ; but we know that every 

 longitudinal fissure must, in this case, be parallel to the sides of the parallelogram, 

 and that thus the whole system must possess the distinctive character of paral- 

 lelism. 



In like manner we may replace the longitudinal fissures of fig. 13 by any other 

 system in which the direction of each fissure, or rather the curve line in which it 

 meets the surface, shall be in accordance with the law distinctly indicated by that 

 diagram. Thus we may take the system represented in fig. 15, where, instead of a 

 single central longitudinal fissure, we have several, and where the lateral fissure ef 



(fig. 13) is replaced by two, e e' and/'/. The law of this system is no longer that 

 of strict parallelism, nor can it be simply described. It is one, however, which is 

 obvious to the eye, and must characterize the whole system formed under the con- 

 ditions contemplated in this case, whatever may be the position of the individual 

 fissures with respect to their distances from the sides or extremities of the district. 

 Of the different systems which might be thus formed and characterized by this law, 

 I have selected one in fig. 15 bearing a close resemblance with the actual district 

 under consideration, to facilitate the comparison between this theoretical diagram 

 and the observed phaenomena. The boundary A B' C has also been varied from 

 fig. 13 for the same purpose. The system of transverse fissures is represented by 

 the transverse lines. 



8. To bring the results of our theoretical investigation to an actual comparison 

 with those of observation, I have further to remark, that, according to our theory, 

 all the secondary pheenomena of elevation, such as faults, anticlinal lines, lines of 

 curvature, &c., are the immediate consequences of the primary phsenomena of 

 fissures, and must, therefore, follow corresponding laws. Hence the lines, repre- 

 senting fissures in fig. 15, may represent the corresponding lines of elevation, such 

 as constitute the objects of direct observation. To test the accuracy of our theory, 



