1922] Hudson: Geology of the Cuyamaca Region of California 231 



ferentiation processes. In most cases one finds even in rather small masses a 

 whole series of different varieties, often of rather dissimilar chemical com- 

 position.sa 



(5) There is not a mathematic proportionality between the size of the gabbro 

 fields and the amount of ore contained in them. However, it may be said that 

 the ore masses in very small gabbro fields are always rather unimportant, and 

 that the larger ore concentrations are all in the larger gabbro fields. ... In 

 gabbro fields of less than 1000 square meters area the ore bodies appear to be 

 unimportant. With an area of 3000 square meters, however, the sulphide de- 

 posits are sufficient for work on a small scale. In gabbro fields of 50,000 to 

 200,000 square meters, that is, 0.05 to 0.2 square kilometers, we find many of 

 the larger sulphide segregations of the Scandinavian peninsula. Finally the 

 gabbro fields measurable in miles are only exceptionally wont to carry sulphide 

 segregations.3 7 



(6) The gabbros of southern Norway, leaving out of account the anorthosite 

 and the saussurite gabbro, may be divided in two great petrographic groups: 



(1) olivine hyperite (olivine + diallage + plagioclase, with ophitic texture); 



(2) norite (rhombic pyroxene -f- plagioclase, with eugranitie-granular texture) 

 with " gabbro-diorite, " which in general is thought to be uralitized norite. 

 The olivine hyperite has here and there "oxide" segregations of ilmenite- 

 enstatite. Further, there are apatite-rutile dikes, formed by ' ' irruptive after 

 effects. ' ' The norite, however, is the mother rock of the most important sulphide 

 segregations of nickeliferous pyrrhotite. 38 



(7) In most gabbro areas we observe normal pegmatitic granite dikes. Also 

 dikes of pegmatitic, granite-like rock, carrying characteristic nickeliferous 



pyrrhotite The latter type of dike, the so-called oligoclase-granite dike, 



contains at Eomsaas, according to Meinich, nickeliferous pyrrhotite, chalcopy- 

 rite, hematite, tourmaline, garnet, biotite, oligoclase, and quartz. The nickel 

 and copper content are high enough so that the dike has been mined. In a 

 similar dike at Erteli the ores and ferromagnesian minerals are concentrated 

 on the borders of the dike, while the later crystallized plagioclase and quartz 



are in the center From the characteristic content of copper and nickel 



one may say with certainty that these dikes originated from splitting processes, 

 in a similar way to the nickeliferous pyrrhotite concentrations. so 



(8) There is a regular relationship between the absolute nickel content of 

 the pyrrhotite on the one hand and the proportion of nickel to copper on the 

 other. The higher the nickel in the pyrrhotite the lower the copper in pro- 

 portion to the nickel.*o 



(9) In the segregations of magnetite and ilmenite not only the titanium 

 iron oxides but also the ferromagnesian silicates are concentrated. Generally 

 there is no corresponding phenomenon in the sulphide deposits, the ratio between 

 ferromagnesian silicates' and plagioclase being as a rule the same both in the 

 pyrrhotite-norites and gabbros as in the normal, sulphide-free rocks. 41 



Other observations made by Vogt having more or less bearing on 

 his conclusion are : 



(1) In the pyrrhotite-norites and pyrrhotite-gabbros the pyrrhotite always 

 reaches a solid condition at the end, after the individualization of the ferro- 

 magnesian silicates and the feldspars. It follows from this that the rhombic 



36 Ibid., p. 134. 



37 Ibid., p. 141. 



^ Ibid., p. 132. 

 so Ibid., p. 135. 



Mlbid., pp. 129 and 264. 

 *i Ibid., p. 138. 



