130 G. IV. Ti/rrell — Alkaline Igneous Rocks, West Scotland. 



ulkali-dolerite also occurs around tlie margin of the Coal-measure area 

 of Dalmelliugton. 



Despite minor irregularities, therefore, there appears to be a well- 

 marked concentric distribution of the various types, in interrupted 

 zones, with reference to the central volcanic area of Mauchline. 

 Although the point needs confirmation by chemical analysis, it is 

 probable that the Mauchline lavas are the effusive equivalent of the 

 kylites rather than any other group. 



This distribution provides a clue, not only to the relative ages of 

 the main types, but also to the age of the suite considered as a whole . 

 It is obviously distributed in relation to the lavas of the Mauchline 

 tract, which overlie the Upper Red Sandstones of the Carboniferous, 

 and are believed to be of Permian age. The widespread teschenites 

 may represent the assumed parent-magma or one of the first 

 differentiates from that magma. They were intruded into the lower 

 levels of the adjacent strata, and were probably prior to the effusive 

 phase. The highest horizon cut by them is the Coal-measures in the 

 east of Glasgow. Here they are much faulted, and are without doubt 

 of Late Carboniferous age.' The kylites, alkali-dolerites, and analcite- 

 syenites may then be secondary or tertiary differentiates derived 

 from subsidiary magma-basins intruded into the higher sedimentarj^ 

 levels at a later date, and accompanied by an effusive phase which 

 gave rise to the Mauchline lavas. 



The suite may therefore be assigned with much probability to the 

 close of the Carboniferous period. Possibly the later members belong 

 to the succeeding Permian. The Mauchline lavas have been assigned 

 to the Permian by Sir A. Geikie.^ Some doubt, however, attaches to 

 the correlation, and there is some probability for the view that the 

 red sandstones which overlie the Mauchline lavas are merely the 

 upper part of the barren red sandstones of the Coal-measures, the two 

 portions being separated by a volcanic episode.^ 



An allied suite of alkaline rocks has recently been described from 

 the Lothians. These are intruded into the sediments above th^ 

 Calciferous Sandstone lavas, and are thus clearly subseqiient to this 

 effusive period. The great majority intrude the Carboniferous 

 Limestone Series. These later basic analcite-bearing rocks are said 

 to bear a great resemblance to some of the lavas of iJurntisland and 

 Bathgate, belonging to the Carboniferous Limestone Series.^ 



It still seems questionable, however, whether some of the alkaline 

 intrusions of the Lothians and Fife may not be linked on ultimately 

 with a later volcanic episode than that of the Calciferous Sandstone or. 

 the Carboniferous Liuiestone. The famous ' Permian ' volcanic vents 

 of the Fifeshire coast, so well described by Sir A. Geikie,® are doubtless 

 contemporaneous with the volcanic episode of the Mauchline district. 

 The lavaforra products have a striking similarity, although so far as 

 is yet known, nepheliue-bearing rocks have not been met with in the 



' Mem. Geol. Surv., The Geology of the Glasgoiv District, 1911, p. 112. 



- Ancient Volcanoes of Great Britain, vol. ii, p. 53, 1897. 



^ Tyrrell, Trans. Glasgow Geol. See, vol. xiii, pt. iii, p. 314, 1909. 



^ Mem. Geol. Surv., Geolor/i/ of East Lothian, 1910, p. 104. 



•' Ibid., Geology of East Fife, 1902. 



