394 Dr. MacCulloch on a Vein in Limestone. 



The inspection of the drawing will show more readily than any 

 description, that the vein consists of a series of separate fragments, 

 having somewhat of a general parallelism, with a correspondence 

 at any two neighbouring extremities, such, as to render it a matter 

 past doubt that they have once formed a continuous line.* To 

 displace such a vein into its present position must have required a 

 series of slides or shifts, each advancing by nearly a similar space 

 beyond the one preceding it. But this sort of echellon movement 

 will be very visible in an outline or diagram in which I have at- 

 tempted to replace the vein in its original position, and also to 

 trace the aligne.ment on which each part must have moved to its 

 present place. 



The deficiency of parallelism occurring in this diagram arises 

 from my having intentionally left the replaced ends at a small dis- 

 tance, that their correspondence might be more visible. 



There is now no appearance of slide or fissure, or discontinuity 

 of any sort in the mass, but the texture of the whole is uniform 

 and continuous. As the specimen has been completely and highly 

 polished, there can be no doubt respecting the accuracy of this 

 observation. It may afford matter for speculation to inquire in 

 what condition the rock must have been to have undergone this 

 change. It has probably consisted originally of a series of thin strata, 

 which having been at some subsequent period fissured at an angle, 

 have admitted the infiltration of the white carbonat of lime which 

 now constitutes the vein in question. That it was perfectly hard 

 at the time of this change the angularity of the fragments show?. 

 The same solution which filled the vein has probably joined the 

 laminae, and cemented the whole once more into a solid mass, al- 

 though the junctions are no longer visible. 



* PI. 26. Fig. 1, 1. 



