CONNEXIONS OF NEPTUNIAN AND PLUTONIAN ROCKS. 49 



the junction would be so complete that there would be no 

 line of distinct separation exhibited by the two masses in 

 contact. Such are the changes which plutonic rocks are 

 found to undergo when in contact with those of aqueous 

 origin. Neptunian Rocks are variously affected by those 

 of ignigenous formation, and very few instances can be ad- 

 duced, where the structure is not in some degree changed : 

 it may only be slightly altered ; but on minute examina- 

 tion changes are more or less apparent. 



Of the three chief rocks, Sandstone, Shale, and Limestone, 

 the various alternations of which form the secondary series of 

 the Lothians, the states of change are innumerable. When 

 the sandstone, whether it be white or red, is in contact with 

 rocks of the trap series, it either acquires the characters of 

 hornstone, jasper, or granular quartz-rock ; and, of course, 

 between all these extremes, there are many different stages 

 of alteration. The changes which are produced upon the 

 various shales are also of great variety ; all are altered in a 

 greater or less degree, the extreme of the alteration being 

 observable in those cases where the shale assumes the cha- 

 racters of flinty-slate or Lydian stone. In the case of the 

 indurated shales, it very generally happens, that although 

 the hardness, fracture, and other external mineral characters 

 are changed, there still exist the remains of a schistose ar- 

 rangement, and when layers of the shale are of various 

 colours, the rock assumes much of the appearance of the 

 Striped Siberian Jasper. The characters which the lime- 

 stone assumes, when in contact with the unstratified rocks, 

 are in some places of the most interesting description ; it is 

 however, to be remarked, that this rock is less frequently 

 than any other member of the stratified series in connec- 

 tion with such masses ; when, however, there is a change, 

 it is similar to that exhibited in other districts, the limestone 

 vol. VIT. I) 



