Yol. 6g.~] VOLCANIC ROCKS OF THE FORFARSHIRE COAST. 473 



rhombic pyroxene has been found in the lavas from Lunan Bay to 

 the Red Head. 



(2) Order of eruption of the different types. — The 

 stratigraphical succession of these varieties of lava appears to be 

 as follows : — 



Latest eruptions (Red Head). Glomeroporpbyritic olivine-basalt, less* basic 

 than usual. 



(Slight unconformity.) 



Normal type of olivine-basalt, with pbenocrysts 

 of olivine, only. 



(Slight unconformity.) 



Olivine-basalt, with pbenocrysts of basic 

 labradorite, and olivine confined to the- 

 ground-mass. 



Normal olivine-basalt. (Base not seen.) 



Cairnconnan Series 

 of sands 



Normal olivine-basalt. (Upper limit not seen.) 

 Olivine-basalt, with pbenocrysts of olivine, 



labradorite, and sometimes pyroxene. 

 Enstatite-basalt, with pbenocrysts of enstatite 



and basic labradorite. 

 Olivine-basalt, with pbenocrysts of olivine, 



labradorite, and pyroxene. 

 Olivine-basalt, with pbenocrysts of olivine and 



labradorite. 

 Normal olivine-basalt. 



Gap due to a fault. 



Enstatite-basalt. 

 Normal olivine-basalt. 



Gap due to a fault. 



n Olivine-enstatite-basalt, with pbenocrysts of 

 Earliest eruptions exposed labraclorite and enstatite, and olivine in the 

 (near Montrose). ground-mass. 



(3) Minerals present. — Felspar. The phenocrysts vary in 

 composition from medium to basic labradorite. They are often 

 quite fresh, exhibiting twinning of albite, Carlsbad, and pericline 

 types. In some rocks, however, they are so much altered as to be 

 incapable of determination. The commonest alteration-products 

 are calcite and chlorite. 



Glass inclusions are common. 



The felspar-crystals of the ground-mass are frequently twinned, 

 and prove to be labradorite of a less basic type than the 

 phenocrysts in the same rock. 



2i2 



