A Note on the G-eology of G-ough Island. 261 



(No. 3). It was evidently water-laid, containing small 

 rounded lapilli and scorise arranged along liorizontal lines 

 of stratification. 



Specimens of the lava which had overflown this tuff were 

 taken from various points (Nos. 2, 4, 7, and (?) 6). In their 

 naked eye appearances these varied considerably, but I was 

 unable to make out any definite succession of flow. All 

 appeared, however, to be lavas, not intrusive sheets. 



Another fragmental rock of very localised occurrence was 

 found on the right bank of the stream, between two dykes, 

 each about 2 feet thick, and running parallel to the shore, 

 6 to 8 feet apart. This was of a bright red colour, contain- 

 ing numerous crystals of felspar, and was seen only in the 

 narrow outcrop on the bank of the stream between the two 

 dykes. It was friable, and gave one the impression of being 

 a volcanic ash (No. 10) which had accumulated in the hollow 

 between the dykes subsequent to their formation. Its 

 strictly limited occurrence between the dykes made one 

 wonder whether it was not a decomposition product due to 

 their influence, but there were no signs of it along the lines 

 of contact with the dykes on either side. It may, however, 

 have been the slaggy surface of one of the lava flows through 

 which the dyke ran. 



On the rising slope on the right bank of the stream there 

 was a coarse agglomerate composed of boulders firmly 

 cemented together by scoriae, so as to form a compact mass 

 as hard as the solid lava. Many of the boulders were rather 

 rounded, and I am inclined to think it had been formed 

 under water, although I could not fully satisfy myself on 

 this point. Some of the rocks in this agglomerate had a 

 very white weathered crust (No. 8), and were at first mis- 

 taken for a quartzite, but on exposing a fresh surface they 

 were found to be volcanic in nature. As numerous white 

 patches of rock had been noted from the ship at various 

 parts of the coast, it is possible that this agglomerate has a 

 fairly wide distribution throughout the island. 



In addition to the double dyke already mentioned, a large 

 dyke, about 6 feet wide, cropped out on the shore to the 

 north of the peperino (No. 9). This dyke ran at about right 



