The Glaciation of the Shetland Islands. 65 



the map), the including rock is a dark reddish -brown norite. 

 The ore contains much chlorite, as shown by the grey-green tinge of 

 its powder, and the green colour of transmitted light when in very 

 thin slices. With it there are also garnet and some fibrolite in 

 minute short needles. South-east of this locality (at v and iv on the 

 map) other openings have been made. Thin magnetite beds occur 

 also on Cruger's Point, in the soda-granite and quartz-diorite, half 

 a mile west of the railroad station. The material is fine-grained, 

 nearly black in colour, chloritic like the preceding, and is usually 

 associated with black mica. These beds are the subject of special 

 descriptions beyond. 



Among the localities in eastern Cortland, three are situated in a 

 ridge or mountain running northward from Colabaugh Pond. One 

 is at the southern end of the ridge, just north of the pond ; another, 

 near the road crossing it, about a mile farther north ; and the third, 

 at the north end of the ridge, nearly three miles from the pond, 

 south of " Summer Hill." The magnetite, at each of these places, 

 contains some disseminated corundum, making it a serviceable 

 emery, and two of these mines have been worked for the emery ; 

 much of it also is chloritic. Fibrolite in small needles and divergent 

 tufts is found with the ore at each locality. 



{To be continued in our next Numier.) 



III. — The Glaciation of the Shetland Isles. 



By B. N. Peach, F.G.S., and J. Horne, F.G.S., 

 of the Geological Survey of Scotland. 



Eeply to Mr. Milne Home's Presidential Address before tlie Edinburgh Geological 

 Society, May, 1880. 



IN his valedictory address as President of the Edinburgh Geo- 

 logical Society, at the close of the session 1879-80,^ Mr. 

 Milne Home reviewed our recent paper on " The Glaciation of the 

 Shetland Isles." - In his address he not only called in question our 

 conclusions regarding the direction of the glaciation of these islands, 

 but likewise referred to the discordance between the observations of 

 Mr. G. W. Peach and ourselves. As much of this adverse criticism 

 is based on a misconception of the real nature of the evidence bear- 

 ing on the question, we are anxious to reply to some of the points 

 in the address which might mislead those who are unacquainted with 

 the subject. 



In our paper we endeavoured to show that there were at least two 

 periods of glaciation in these islands ; the one being coincident with 

 the climax of the Ice age, during which the islands were buried 

 underneath the Scandinavian mer de glace, while the other was 

 characterized by local glaciers which radiated from the high grounds 

 in the ordinary way. We stated as the result of a careful examina- 



1 Trans. Edin. Geol. Soc. vol. iii. part 3, p 357. 

 ^ Quart. Joui-n. Geol. Soc. vol. xxxv. p. 778. 



DECADE II. — VOL. VIII. NO. II. 5 



