REPORT OF MEETINGS FOR 1901 53 



But the principal feature to be dealt with before we leave 

 this part of the subject is the geological history of The Bass. 

 Briefly stated it is as follows : — At a late period in the history 

 of the Lower Carboniferous volcanic rocks of East Lothian, 

 small eruptions seem to have taken place at many different 

 centres, instead of being confined to one or two larger volcanoes. 

 Hence arose several small volcanoes, somewhat like the Puys 

 of Auvergne ; or else, perhaps, like some of the numerous 

 parasitic cones which occur on the flanks of Etna. The last 

 products of volcanic eruption to rise through these were 

 different, as regards their chemical composition, from those 

 which preceded them. Most of the lavas from the East 

 Lothian volcanoes were of the kind that geologists term 

 andesites — because it is the prevailing type in many of the 

 South American volcanoes. But another type, containing 

 but very little felspar, was intruded underground during the 

 earlier phases of eruption. This type of eruptive rock, which 

 is particularly-well seen in the cliffs and on the shores east 

 of Canty Bay, may be called a Limburgite. It is a variety 

 of basalt in which the proportion of felspar present is unusually 

 small. The east landing place at Canty Bay is on a sill of 

 rock of this kind. The very latest phases of volcanic action 

 gave rise to another kind of eruptive rock, which, chemically 

 considered, stands almost at the opposite extreme as com- 

 pared with the Limburgite, This rock contains a very large 

 percentage of felspar; in fact, the rock consists of very little 

 else, and much of the mineral belongs to that potash felspar 

 known as Orthoclase. An eruptive rock of such composition, 

 which has been formed at or near the surface, is usually 

 spoken of as Trachyte. The Rock of The Bass is of this kind. 

 It used to be regarded, as one may see by looking at the 

 Geological Survey maps, as a "greenstone"; but, about ten 

 years ago, I had an opportunity of landing on it, and at 

 once saw that it was certainly not a " greenstone." L)r Hatch, 

 who examined my specimens, at once pronounced the rock 

 to be a true Trachyte. This proved to be the case also with 

 the rock of North Berwick Law. In all essential respects 

 the rock composing Traprain Law is of the same nature ; 

 but, in addition to the felspar, it contains traces of a mineral 

 called Nepheline, and hence it is called a Fhonolite by those 



