244 THE CRYSTAL PALLS IRON-BEARING DISTRICT. 



as ail accessory. Ilnienite occurs in irregular masses in rod-shaped pieces: 

 Spliene is present in original grains and also as a secondary product after 

 ilmenite. Apatite occurs and is sometimes included in the sphene. 



The most striking feature of the rock is its textural variation. Some 

 of the sections show very good granular texture; others have a fair ophitic 

 texture; the most common is a striking parallel texture which macroscopic- 

 ally gives to the rock a schistose appearance. This may be seen even in 

 the same section with the ophitic texture, the two grading into each other. 

 The parallel texture is occasioned by the arrangement in a common direc- 

 tion of the long diameters of nearly all of the minerals (figs. A and JB, PI. 

 XLII). The grains of sphene often lie in long trains agreeing with this 

 general parallelism. One's first idea would probably be that the texture was 

 due to the cause which has produced parallel structures in most other ancient 

 POcks — pressure. However, it can not be referred to this, as the minerals — 

 with some individual exceptions — show slight or no pressure effects. 

 Apparently the only explanation borne out by the facts in this case is that 

 we have to do with a fluidal texture, produced by the movement in the 

 magma consequent upon its injection along the fissures in the gabbro, the 

 parallelism of the minerals agreeing with the bounding sides of the fissure. 



BRONZITE-NORITE DIKE. 



The main hornblende-gabbro and the fine-grained dikes just described 

 are cut by a dike, about 3 feet wide, of coarse rock which resembles that 

 forming the main mass of the knobs in every way except that it contains a 

 very much altered orthorhombic pyroxene (bronzite) in greater quantity 

 than the hornblende. The rock is a very pure kind of bronzite-norite (fig. 

 B, PI. XLIV). The following analysis (No. 1, Sp. 23755), by Mr. George 

 Steiger, shows the gabbro affinities of the rock. The high percentage of 

 magnesia gives a clear indication of the important role played by the bron- 

 zite in the composition of the rock. 



With the analysis of the bronzite-norite there is placed for comparison 

 an analysis (No. 2) of a norite from Ivrea, Italy, which is essentially the 

 same as the above in mineralogical as well as chemical composition. In 

 the Italian rock hypersthene, instead of bronzite, is the chief pyroxenic 

 constituent.'^ 



' Petrographische Untersuchungeu iiber die iioritisclieu Gesteine der Umgegond von Ivrea in 

 Oberitalien, by F. R. van Horn : Tschermaks mineral, Mittbeil., Vol. XVII, 1897, Part V, p. 404. 



