ASSOCIATED MET AMORPHIC ROCKS OF THE LAKE-DISTRICT. V 



The following are the results at which Prof. Euchs arrives in the 

 memoir quoted, which deals with a set of rocks apparently very 

 similar to those around Skiddaw : — 



"While the metamorphism of the clay slate generally increases as 

 the granite is approached, yet do alternations occur of beds in all 

 stages of metamorphism. 



The metamorphism begins with the appearance of little specks 

 (concretionary), which pass into andalusite and chiastolite ; and the 

 rest of the rock-mass passes by degrees into an indistinct mixture of 

 mica and quartz with some felspar (mica-schist and gneiss). 



The andalusite and concretions are still met with in the mica-schist 

 and gneiss, but are at last changed by pseudomorphism into mica. 



The cause of these mineral changes is, first of all, molecular arrange- 

 ment ; and afterwards an interchange of chemical constituents comes 

 in to help. "When the clay slate is changed into mica-schist and 

 gneiss, the superfluous alumina goes to form the concretions and the 

 andalusite. The alkaline earths and iron are decreased in quantity, 

 but the alkalies and silica are increased. 



There is a perfect petrographical passage in many places from the 

 gneiss into the granite. The organic matter of the clay slate gradu- 

 ally disappears during the process of metamorphism ; but traces of it 

 can be found in all stages of the alteration and even in the granite 

 itself. 



The elaborate memoir by Durocher upon metamorphism, quoted 

 above, tends as follows : — 



For the idea of semifusion he substitutes that of a flow of secular 

 heat emanating from below and from centres of plutonic action which 

 perhaps did not even attain to dull red heat. Two kinds of meta- 

 morphism are distinguished — that resulting from a movement of the 

 particles composing stratified beds, and that produced by the intro- 

 duction of a foreign body playing the part of a cement and penetrating 

 to the interior of the rocks, as carbon does to iron. Generally the 

 igneous rocks develop in the adjacent beds just those minerals of 

 which they are themselves composed. 



Carius describes the metamorphism of clay slate around granite 

 masses, near Eichgriin. At a certain distance from the granite the 

 rock is full of small concretions (spotted schist), and becomes more 

 and more micaceous the nearer the granitic mass is approached. He 

 gives the following analyses of six specimens of these rocks : — 



1. 2. 3. 4. 5. 6. 



Silica 59-385 60028 60-605 63-174 60-005 61-387 



Alumina 22069 19113 24-055 19-288 24104 20803 



Iron oxide 6816 7373 5 687 4935 6436 6606 



Manganic oxide 0-273 0141 0280 0537 0-137 0246 



Lime 0-236 1-165 0-412 0388 0-173 0903 



Magnesia 3-608 2186 1781 1-599 1-872 2-105 



Soda 2-109 3-198 0*776 1829 2-087 3-262 



Potash 3-849 3785 3648 4193 2 797 2966 



Water 3 471 3-993 3 305 3 962 2-752 1476 



101-816 100982 100-349 99905 100 363 99754 



