Vol. 69.] VOLCANIC ROCKS OF THE FORFARSHIRE COAST. 463 



of sediment, similar to the matrix of the conglomerate. The 

 conglomerate dips southwards under an escarpment of compact 

 lava, 10 to 15 feet high. A number of spheroidal masses of 

 volcanic rock about 2 feet in diameter, which exhibit concentric 

 amygdales where broken across, occur in the lower portion of 

 this lava. They are embedded in compact lava, and are the best 

 examples of 'pillows' that I have observed along this coast, although 

 a rude pillow-structure is not uncommon. The upper portion of 

 the lava becomes more amygdaloid al, though lenticular amyg- 

 daloidal patches occur within the more compact mass, and towards 

 the top it is of a brick-red colour and much intersected by fissures 

 filled with green sandstone. 



A somewhat remarkable exposure of conglomerate occurs about 

 half a mile north-east of Fishtown 

 Fig. 2. — Plan of the jurx- of Usan. The conglomerate rests 

 Hon between conglomerate on an irregular surface of volcanic 

 and lava, north-east of rock, apparently filling in a network 

 Fishtown of Usan. of valleys. The junction between 



the two is sometimes vertical and 

 ', quite irregular in plan, though not 

 o 1 faulted, one example appearing as 

 y i shown in the appended tig. 2. 

 o i All the boulders examined in this 



i« conglomerate were volcanic rocks of 

 conglomerate ° 1^ a type characterized by felspar- 

 phenocrysts. 

 1 The cliffs commence at Fishtown 



| of Usan, and continue almost with- 

 ; out a break as far the sands of 

 °Y Lunan Bay. 



Immediately east of Fishtown a 

 great wall of rock rises about 50 feet above the shore, and is 

 separated by a narrow gap from the cliff. It consists partly of a 

 dyke 1 and partly of the lavas into which the dyke was intruded. 

 The dyke is about 6| feet wide, and is a brownish-red rock with 

 fairly large felspar-phenocrysts and some green amygdales. This 

 rock is a porphyrite, and is easily distinguished by its felspars 

 from the lavas into which it is intruded, as also by the absence of 

 the sandstone-filled fissures and clinker-beds which are so charac- 

 teristic of the latter. 



"West of the harbour of Fishtown of Usan, the olivine-basalts are 

 succeeded by a type of volcanic rock which is characterized by large 

 plagioclase-phenocrysts, as also abundant red and green amygdales. 

 This new type of lava, an enstatite-basalt, is a famous 

 hunting-ground for agates and other secondary minerals, 2 and the 

 upper portion of each sheet is seamed by fissures filled with pale- 



1 Geol. Surv. 1-inch map, Sheet 57. 



2 M. F. Hedclle, 'Mineralogy of Scotland' 1901, vol. i, pp. 75-76, 106, 131, 

 &vol.ii, pp. 140, 146. 



