IxXXvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. Ixxiii, 



of intrusion ; but in West Lothian, West Fife, and Stirlingshire 

 important volcanic groups appear in the Carboniferous Limestone 

 Series, and farther west vulcanicity continued in some districts into 

 the Uppei- Carboniferous. In the com'se of the revised survey of 

 the ground Dr. Flett, Mr. Barrow, and Mr. Bailey have added 

 much to our knowledge on the petrographical side. The volcanic 

 rocks are mostly of basic composition. Not every type of basalt 

 bears the evident mark of richness in soda, but their constant 

 association with mugearites and tmch3^tes is always significant. 

 Intercalated among the lavas, with corresponding tuffs and agglo- 

 merates, the same types occur in the form of sills, which must 

 have been intruded during the volcanic period. Sills and dykes of 

 later intrusion belong to other petrographical types with more 

 strongly marked alkaline characters. They include phonolites, 

 analcime-dolerites, essexites, teschenites, and picrites, and in smaller 

 occurrences analcime-basalts, monchiquites, and limburgites. 



In the eastern districts these alkaline rocks were apparently 

 intruded in Carboniferous Limestone times. Similar intrusions in 

 the west may be in part of like age, but some in Ayrshire are 

 found in sti-ata as high in the succession as the latest Carboni- 

 ferous, if not higher. Further, these Ayrshire intrusions, or some 

 of them, are younger than, and evidently related to, the volcanic 

 group of the Mauchline basin, interstratified among red sandstones 

 which were assigned by Sir Archibald Geikie to the Permian. 

 Whether of Permian or of uppermost Carboniferous age, this 

 interesting volcanic outbreak is to be regarded as a pendent to the 

 Carboniferous igneous activity of the area. As described by 

 Mr. Gr. W. Tyrrell, the Mauchline lavas are all of very basic com- 

 position, and include olivine-basalts, sometimes approximating to 

 limburgite, analcime-basalts and monchiquites, and fresh nepheline- 

 basalts. The intrusive rocks, besides essexites, teschenites, and 

 picrites, comprise a number of peculiar types very rich in nepheline 

 or in primary analcime. The group as a whole marks the final 

 stage of the increasing alkalinity of the Carboniferous suite. 



Of the Thornhill volcanic rocks, in Dumfries -shire, which Sir 

 Archibald Geikie correlates with the Mauchline group, we have as 

 yet no petrographical account ; but in the numerous small volcanic 

 necks, with associated dykes and plugs, on the coast of Fife, also 

 assigned to the Permian, there are monchiquites and nepheline- 

 basalts closely comparable with those of Ayrshire. It is not 

 improbable too that at this late Palaeozoic epoch diffused igneous 



