472 BR. A. JOWETT ON THE [Oct. I9I3,, 



another rock, practically identical with it petrographically, and! 

 occupying a similar stratigraphical position (that is, with the same 

 conglomerate below and above it), crops out at the foot of the cliff" 

 farther south. The upper portion of this lava is amygdaloidal. 



The conglomerate preserves its hummocky surface in a very 

 striking manner when it is buried in the overlying red sandstones, 

 which first appear at the top of the cliff immediately south of Ptock 

 Skelly. The sandstone is current-bedded around the mounds, but 

 quite evenly bedded above them, dipping away steadily southwards. 



The conglomerate itself is by no means uniform in texture, 

 sometimes including fairly thick bands of red sandstone and of finer 

 conglomerate : these, however, were often partly removed by the 

 stronger currents which brought the larger boulders that make up 

 the coarser part of the deposit. On the whole, the conglomerate 

 appears to thin out northwards. 



Farther south, higher beds of red sandstone, shale, and con- 

 glomerate attain a great thickness in. the cliffs, and all appear to 

 contain more or less volcanic debris. The beds of conglomerate 

 increase in thickness, and their boulders increase in size towards the 

 south, consisting almost entirely of volcanic rocks with occasional 

 angular and subangular pieces of red sandstone. They are covered 

 by thick beds of sandstone, which, higher in the series, include 

 pebble-beds of an entirely different character, containing a pre- 

 ponderance of well-rounded pebbles of quartzite, in addition to those 

 of volcanic origin. 



III. Petrography oe the Igneous Rocks. 

 (a) Lavas. 



(1) Petrographical types. — The distribution of the various 

 types of lava is indicated on the sketch-maps (figs. 1, 3, & 4, pp. 460, 

 464, & 468). 



The enstatite-basalt is the only type from which olivine is 

 absent, and, although it occurs for a considerable distance along the 

 coast north of Lunan Bay, it constitutes but a small fraction of 

 the lavas between Montrose and the Eed Head. 



The oli vine-basalts may be divided into two main groups, 

 according as olivine occurs in the form of phenocrysts, or is entirely 

 restricted to the ground-mass. The former group is the more 

 abundant, the latter including two varieties only : one with 

 enstatite and plagioclase-phenocrysts (near Montrose), and one 

 with plagioclase-phenocrysts only (near Ethie Haven). The most 

 abundant variety in the former group has, broadly speaking, no 

 phenocrysts except olivine, augite occurring in the ground-mass with 

 felspar and iron-oxides ; although in other varieties phenocrysts 

 of (1) labradorite, (2) labradorite and augite, and (3) labradorite 

 and rhombic pyroxene occur, in addition to the olivine-phenocrysts. 



One variety is full of glomeroporphyritic aggregates of olivine, 

 augite, and labradorite (South Mains and Eock Skelly). JSTo 



