56 



HANS REUSCH. 



[No. 7. 



argillaceous mica-schist with joints parallel to and at angles to 

 the cleavage. Several cases are remarkable in which the 

 cleavage may be sliown to have been folded. The second fig. 

 p. 19 shows a section one metre high through changing layers 

 of light and dark clay-schist. On account of the folding the 

 schistosity now is fanshaped. The rock shown in the following 

 drawing consists of sandy argillaceous mica-schist. Certain layers 

 of this are penetrated by small plates or veins of quartz and 

 calcspar parallel to the cleavage. The fan-shaped position of 

 these veins shows even at a distance the folding of the cleavage. 

 The formation of false schistosity is often connected with a fine 

 crumpling of the strata. The sandstone shown in the first fig. 

 p. 21 is penetrated by membranes of sericite by which false 

 schistosity is produced. The layers a. a. are especially full of 

 sericitic membranes. Farthest to the right is a folded plate 

 of white limestone x. x. It is uncertain whether it is a bed or 

 a vein parallel to the bedding. 



The hand- piece depicted in the second fig. p. 21 shows a 

 layer of sandstone like rock a, enclosed in argillaceous mica-schist 

 b. The cleavage is parallel to the flat front of the hand- piece. On 

 b. are seen fine stripes; it is a stretching structure which ap- 

 pears as a fine undulation. The following fig. shows a micro- 

 scopic section; in the upper part we see the sandstone-like 

 layer which upon a closer examination is seen to be Very little 

 like a sandstone. Calcspar occurs here plentifully; the rest of 

 the white on the diagram is a fine-grained mixture of felspar 

 (partly with twin-stripes) and quartz. The shaded mineral which 

 is especially plentiful in the lower part of the fig., the argil- 

 laceous mica-schist, is a faint greenish muscovite. The stretching 

 structure is noticeable under the microscope mainly on account 

 of many of the muscovite sections being parallel to it. 



