108 



whole series. This is probably owing to the nature of the rock, 

 which, being a highly crystalline greenstone, must have passed slowly 

 from a state of fusion. The stratification of the sandstone is 

 obliterated through a space of seven or eight feet, and this rock 

 assumes the structure of a claystone. The case is strongly in favour 

 of the view often advanced, that the Arran claystones are merely 

 metamorphic sandstones. Intersecting this dike is another, ten or 

 twelve feet wide, ranging 37 W. of N., dipping E.N.E., and 

 consisting of compact fine-grained greenstone. It is sunk below 

 the level of the sandstone ; and, on this worn, depressed surface, 

 there rests a boulder of coarse-grained granite, estimated at about 

 thirty tons weight. Now, no force of surging waves, surged they 

 ever so fiercely, is adequate to shift the position of such a mass as 

 this ; and we must, therefore, conclude that the huge boulder now 

 rests where it was originally thrown down by the floating berg 

 which bore it from the granite nucleus. Perhaps, however, it is not 

 necessary to suppose that the dike was then excavated to its present 

 level. It is quite conceivable that as the parts of the dike around 

 the boulder were worn away, its support may have been loosened, 

 and so its position may have shifted a little at long intervals. 



71. In the sandstone of the cliffs overlooking this point we were 

 so fortunate as to discover a very interesting fossil, on our last excur- 

 sion, after the pages containing Art. 62 had been printed off. We 

 refer to a specimen of orthoceras communis, a true carboniferous 

 fossil, the occurrence of which in this locality is strongly in favour 

 of the view we have advanced (Arts. 48, 62), regarding the age of 

 these sandstones. It may, indeed, be urged that carboniferous 

 fossils pass upwards into the lower portion of the Permian (lower 

 new red) system. But we submit that orthoceras is not a genus of 

 which this can be said ; a very few cephalopods, allied to nautilus, 

 being the only animals of this order yet found in the lower Per- 

 mian system. 



Still advancing eastwards, we meet with several other dikes one of 

 these is depressed ten feet in the tideway, is on a level with the sand- 

 stone along the grassy surface at the base of the cliffs, and in the 

 front of the cliff is again worn, forming a deep chasm, which is 

 bounded eastwards by a bold projecting edge of the cliff, crowned 

 with wood. The dike on the beach, and fissure aloft, are about four- 

 teen feet wide each, but not exactly in the same direction, the dike 

 sustaining here a considerable undulation. 



72. We now reach the great bed of claystone, the largest upon 

 this coast, and presenting many interesting appearances. It forms a 



