Geikie — Permian Yolcanos in Scotland. 



245 



of compact sheets and rough, aniygdaloids, 

 as in those wonderful sections of old lava- 

 iiows along the coasts of the Western Islands 

 and the north of Ireland. In the railway 

 cutting at the month of the Mossgiel Tunnel 

 the melaphyres are found in their lower parts 

 to he interstratified with and to rest upon 

 beds of volcanic ash and brick-red sandstone. 

 These strata are well bedded, and are made 

 up of thin alternations of red gravelly trap- 

 tiiff, or peperino, fine ash, and, more or less, 

 ashy sandstone — the whole pointing to, a 

 period of intermittent eruption when showers 

 of dust and lapilli fell upon and became 

 interstratified with ordinary sediment. In 

 the river section at Ballochmyle, described 

 by Mr. Binney and Professor Harkness, a 

 similar red angular tuff (the " breccia " of 

 these geologists) forms a bed at least 30 feet 

 thick, passing up into the red sandstones, as 

 will be more fully pointed out in the sequel. 

 It rests upon the melaphyres, which can be 

 traced to within a few yards frora it when 

 the river is low, though the actual line of 

 junction is not here seen. 



Such are the characters of this group of 

 volcanic rocks round the whole of the ring 

 with which they guxlle the Permian basin of 

 the Ayr. Erom the bedded, slaggy, amyg- 

 daloidal character of the melaphyres, from 

 their interstratification with red sandstone 

 and ashy beds, from the tufi^ which is found 

 both below them and above, it is evident 

 that they are not intrusive masses thrust up 

 among the palasozoic formations, carrying 

 with them little or no clue to their date, but 

 that they have been poured out at the sur- 

 ■face, and must be of the same geological age 

 as the strata with which they are associated. 



Outside the volcanic ring there occurs a 

 number of small rounded hills or hillocks, 

 consisting of a coarse red volcanic agglomerate 

 (d in Fig. 1). This rock is unstratified and 

 presents a very tumultuous appearance. It 

 is made up of fragments of various melaphyres 

 of all sizes, up to masses a yard or more in 

 length, angular, subangular, and rounded, 

 imbedded in a gritty, ferruginous, felspathic 

 paste, in which scattered crystals of augite, 

 melanite, and black mica occur. As a rule, 



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