Some occurrences of leucite in East Lothian

Abstract

The occurrence of the mineral leucite among the igneous rocks associated with the Scottish Carboniferous Succession has so far been established in a single instance only, namely, that recorded by D. Balsillie (1936, p. 16) who described a leucite-basanite from the East Lothian coast. This rock occurs in the form of two small intrusions in a vent, the whole forming a promontory known as The Great Car, situated about four miles east of North Berwick. It is to be recalled, however, as Mr Balsillie points out, that the former presence of leucite had previously been suspected by E. B. Bailey (1910, p. 126) in the kulaite lava of Blaikie Heugh which lies between seven and eight miles inland to the south. This feature of the kulaite will be discussed below in comparison with the occurrence of leucite in another East Lothian lava, hitherto undescribed. This rock, which occurs in the North Berwick district, shows many mineralogical resemblances to that of Blaikie Heugh and has accordingly been classified as a leucite-kulaite. Yet another rock which may originally have been closely akin to these lavas occurs as inclusions in the phonolite laccolith of Traprain Law, a prominent landmark less than a mile north of Blaikie Heugh. These inclusions will be described in some detail as they contain structures which are strongly reminiscent of the pseudoleucites described by J. F. Williams (1890) and others. Except for the Car rock from which Mr Balsillie reports fresh leucite, the occurrences of the mineral in East