54 Hocks of Noyang. 



into a very pale yellow epiclote. In several cases there are 

 crystals remarkable for being partly composed of felspar and 

 augite, the latter being interposed so that the axis "c" 

 coincides in each case, and the angles formed by the plane 

 of vibration in the two minerals are diverse and charac- 

 teristic of each. 



I observed one solitary instance of a very small brown- 

 coloured and dichroic section of a mineral having the pris- 

 matic cleavage of amphibole. It was almost surrounded by 

 a chloritic alteration of augite, and may itself be an alteration 

 product of that mineral. 



(4.) Prisms of apatite plentiful. 



There is no great improbability that a rock such as 

 this should appear among the most basic of the rocks 

 of an area such as Noyang. This dyke occurs under just 

 the same conditions as dykes of the more basic diorites, and 

 the main distinction between it and them is in the more 

 elongated character of the felspars, and the occurrence of 

 augite instead of hornblende. 



This rock terminates the series which I have collected to 

 illustrate the igneous rocks of Noyang. The whole series is 

 parallel to that of which the quartz-porphyries are character- 

 istic, the only difference being in the preponderance, in the 

 Noyang group, of a soda felspar, and in the other of a potassa 

 felspar. The presence of albite, or of an oligoclase standing 

 very near to it, as the characteristic felspar of this series is 

 peculiar ; and it is interesting to observe that, taking the 

 crystalline-granular rocks as the starting-point, there is a 

 decrease in basicity from an oligoclase to albite, and at the 

 same time a more marked decrease in the general basicity of 

 the rock by the disappearance of the Mg Fe minerals, so 

 tha.t at the end of the series the white quartz-porphyrites 

 are composed almost wholly of albite and of quartz. 



IV. — The Sedimentary and Metamorphic Rocks. 



The igneous rocks which I have now described form, in 

 the aggregate, a great mass which has left the traces of its 

 intrusion in the changes produced in the physical and 

 molecular condition of the sediments with which it came in 

 contact. 



The normal strike of the Silurian sediments of the district 

 may be taken as about N 30° W, but I find that in the 



