42 GEOLOGY OF THE LOTHIANS. 



distributed through it. The occurrence of magnetic iron- 

 ore in basalt, forms a well-marked character of this rock, 

 while the very general distribution of iron-pyrites through 

 greenstone, appears to characterize it. By assuming crys- 

 tals of basaltic hornblende and glassy felspar, the basalts 

 of some districts frequently acquire an almost porphyritic 

 structure. Though the vitreous state is that in which 

 felspar most, generally occurs in basalt, still in others 

 common felspar appears. At Garry Point, in East Lo- 

 thian., where a finely columnar basalt occurs, the contain- 

 ed crystals are of common felspar. Amygdaloidal cavities 

 abound in some basalts in such quantities, that the rock 

 assumes the perfect amygdaloidal structure. The ba- 

 salt of the Lothians is very generally associated with the 

 columnar arrangement, and, as in greenstone, the columns 

 vary in position and number of their sides. The hill of 

 Arthur's Seat, thelimestone quarry of the Hill-house, in Lin- 

 lithgowshire, and other points, exhibit beautiful groups of 

 these columns. 



Considered as a group, the augitic rocks of the Lothians 

 are remarkable, when compared with some of the other 

 great formations of the same class which occur in Scotland, 

 in the circumstance of the zeolitic minerals occurring very 

 rarely in them, and then only in comparatively small quanti- 

 ties. Intimately connected with the unstratified rocks of the 

 Lothians, Trap-tufa occurs ; it is composed of rounded and 

 angular masses of limestone, sandstone, slate, and trap, in- 

 closed in a basis of trap, in different states of compactness. 

 In size, the imbedded masses vary from the smallest magni- 

 tude to many yards. It never contains fragments of any rock 

 which occurs in situ at a great distance ; but, on the con- 

 trary, all are in the more immediate neighbourhood of the 

 tufaceous deposit. Much of the country round North 



