OLD RED SANDSTONE VOLCANIC ROCKS OF SHETLAND. 





OOO 



occupying the centre of the syncline. From Stenness northwards towards 

 Hamna Voe this volcanic breccia is traceable, being inclined at a gentle angle 

 to the south of east and on the west side of the synclinal fold the porphyrites 

 reappear, with a gentle easterly dip. They occupy the strip of rising ground 

 bordering the sea at the Grind of the Navir, and in this neighbourhood the 

 terrace-shaped features are most characteristically developed. Along the coast- 

 line, from Stenness to the Grind of the Navir, there is an excellent exposure of 

 the successive lava flows with few intercalations of tuff. The numerous isolated 

 stacks and the more distant islet of Doorholm, which are formed of the same 

 materials, plainly indicate the great denudation which the contemporaneous 

 volcanic rocks have undergone. 



A traverse along the south bank of Rooeness Voe confirms the general 

 arrangement of the strata just described. The fault bounding the interbedded 



Fig. 2. — Four successive lava flows overlaid by tutf. Oukren Head, Rooeness Voe, 

 Rooeness Hill cliff" in the distance. 



series in Rooeness Voe, which has already been referred to, has not produced 

 much effect on the inclination of the bedded masses. A short distance to the 

 north-west of the fault, in a small stream draining two lochans, a section is 

 exposed of red micaceous flaggy sandstone, overlaid by coarse tuff, dipping to 

 the north-west at an angle of 3°. Following the coast-line, we have a con- 

 tinuous exposure of diabase-porphyrites, lying nearly flat or at gentle angles, 

 till we reach Ockren Head at the mouth of the Voe, where the lava flows are 

 admirably shown, piled on each other in regular succession. On the headland 

 and also in an outlying stack to the north, there are four sheets of lava 

 joverlaid by coarse tuff. The diabase-porphyrites present the usual scoriaceous 

 character on the upper and under surfaces of the flows, and they likewise 

 thicken and thin out rapidly. The lavas have a purple tinge, and perhaps 



