502 John Spil/er — Coast Erosion in Suffolk. 



This part of the subject may be summed up by saying that both 

 the dark grey and brown patches strongly resemble in their micro- 

 scopic structure certain altered rocks of the kind commonly described 

 as Diabase, and if taken alone they would be most accurately 

 described as epidiorite. 



I have only one slice of the banded type of inclusion, and this 

 differs entirely from those above described. It consists of an 

 aggregate of flakes of strongly pleochroic brown biotite and grains 

 of magnetite, enclosed in poecilitic fashion in large plates of felspar, 

 w^hich at the margin are continuous with the felspars of the 

 normal granite. These plates are of variable character — orthoclase, 

 microcline, or more commonly plagioclase. 



This is obviously something very different from the cases before 

 described, and I am inclined to regard it as an altered slate fragment 

 caught up during intrusion, and metamorphosed by the granite. 



The foregoing brief descriptions show that these dark patches 

 in all cases possess some of the characters of a metamorphic rock, 

 and it is even possible to form an opinion as to what the original 

 rock may have been. The most promising case is what has been 

 spoken of above as the ' diabase ' type. In these the absence of 

 biotite is sufficient to show that they are not mere centres of con- 

 centration of the basic molecules of the magma, as they do not 

 consist of the same minerals as the rest of the rock in different 

 proportions. The abundance of secondary sphene is also suggestive. 



I therefore conclude that the dark patches in the Mount Sorrel 

 granite are, in all cases yet examined, much altered fragments of 

 other rocks caught up by the magma during intrusion, and I suggest 

 that it is possible to discriminate to a slight extent between those of 

 igneous and of sedimentary origin. 



X. — Eecent Coast Erosion in Suffolk : Dunwich to Covehithe. 



By John Spillek, F.C.S.i 



rpHIS communication brings up to date the record of losses on the 

 \_ Suffolk coast, and continues the report presented at the Ipswich 

 Meeting, 1895, of which details were published in the Geological 

 Magazine for January, 1896. Since that time scarcely a year has 

 passed without the winter gales and high tides doing mischief at 

 one or more points of the coast embraced within the above-mentioned 

 limits ; but whilst Lowestoft and Pakefield, Covehithe and Easton 

 have all suffered very considerably, the cliffs at Dunwich remained 

 until quite recently almost unaffected. 



The losses may be summed up as follows : — 



Dunwich. 

 All Saints Church ruins and graveyard. — The 43 feet of land 



^ Eead before the British Association, Cambridge, Section C (Geology), Aug., 1904. 



