GEOLOGICAL OBSERVATIONS IN SOUTH GEORGIA. 805 



Their total thickness cannot be estimated. There is evidence to show, however, 

 that they are at least 500 to 1000 feet thick in the glacier glen at Cape George, 

 but that may be only a small part of them. 



The Succession and Thickness. 



We can now state the order in which the various rocks succeed each other in 

 South Georgia and the estimated thickness of each of them. 

 Cumberland Bay Series : — 



Upper division. The creamy-white rocks and all rocks 



exposed above the rusty-brown rocks . . .1500 feet 



Middle division. The rusty-brown rocks . . . 3000 ,, 



Lower division. The dark shales, greywackes, etc. . 1200 ,, 



Total thickness exposed . . 5700 feet 



Unconformity. 

 Cape George Series : — 



Greenish-grey rocks with "Augen" structure. Exposed, 



about ....... 500 feet 



The lowest greenish-grey rocks are separated from the Cumberland Bay Series 

 both on account of the unconformity between them and the more severe pressure- 

 metamorphism they have been subjected to in early crustal movements. The 

 three divisions of the Cumberland Bay Series overlying them are apparently in 

 continuous succession. They have been broken, folded, and contorted in various 

 parts of the island, but their original continuity is notwithstanding easily dis- 

 tinguished. Their subdivision into three sections by colour is useful, as it enables 

 us to note the various horizons exposed in different parts of the island, as shown on 

 the geological map and section through Mount Paget (Plates LXXXI and LXXXII). 



Local Distribution of Rocks. 

 Leith Harbour and Stromness Bay. 



The rocks are in every case stratified and of sedimentary origin. They are all 

 more or less indurated, but their original bedding and character is still distinct. 

 Lateral pressure has tilted and folded the strata so that there is no general dip. 



A line of weakness is plainly evident from the centre of Mutton Island (PL LXXXV, 

 fig. l) to the crumpled rock exposure in the centre of the glacier (PI. LXXXIII, fig. 2). 

 This line strikes south-east of Mutton Island and reaches the south shore of Stromness 

 Bay in crumpled strata. The line of weakness was originally a fold in the rocks, 

 with its axis running north-west from Mutton Island to the upper end of Leith 



TRANS. ROY. SOC. EDIN., VOL. L, PART IV (NO. 23). 113 



