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REVIEWS 977 



Dcr Eldolithsye7iit dcr Scrra dc Moncliiquc, seiiic Gang- und C071- 

 tnctgesteme. By K. v. Kraatz-Koschlan and V. Hackman. 

 Tschermak's Mineralogische und Petrographische Mittheil- 

 ungen, Vol. XVI, pp. 197-307, Pis. IV and V. 1896. 



The rock making up the mass of the Serra de Monchique in the 

 southern part of Portugal, first described as "granite" by Bonnet in 

 1850, was later recognized as a new type by Blum in 186 1, and by him 

 given the name foyiiite, from the dominant peak of the range. It is 

 today known as the foyiiite type of the elasolite syenites. The present 

 paper, while largely taken up by detailed petrographic descriptions, is 

 professedly a study of the geological relations of the various rocks. 



The ela^olite syenite massif is roughly elliptical in area, with its 

 longer axis, 15.5 kilometers, extending nearly east and west. Its 

 breadth is about 5.5 kilometers. It consists essentially of two main 

 mountain ridges, separated by the northeast and southwest valley in 

 which the village of Monchique lies. The more easterly of these two 

 ridges takes its name of the Picota from its dominant peak (774 meters), 

 while Mount Foia (902 meters) lends its name to the western ridge. 

 The whole elliptical area is enclosed by the shales and sandstones of the 

 Culm, and the intrusion probably took place within Carboniferous time. 



A zone of contact metamorphism was traced around a large portion 

 of the area, and is assumed to completely surround it. Near the con- 

 tact the normal syenite becomes finer grained, and is either a mica- 

 foviiite, in which the non-micaceous dark minerals have almost 

 disappeared, or has the usual aegirine-augite replaced by segirine. 

 These changes are accompanied by the addition of lavenite, spinel, 

 and tourmaline. The surrounding metamorphosed sediments consist 

 of altered quartzose grauwacke, black hornfels, and knotenfhofischiefer. 

 A cordierite-mica-hornfels which occurs as an inclusion in the elaeolite 

 syenite is regarded as an altered diabase. So-called "diabase horn- 

 fels" occurs in two places in the metamorphic girdle and is assigned a 

 similar origin. The width of the contact zone varies from a few 

 meters to over a hundred meters, but is in general not so wide as 

 would have been expected in the case of an intrusive granite mass of 

 equal size. It is considered that the alteration was conditioned by the 

 temperature of the eruptive mass and not, to any great extent, to 

 pneumatolytic processes. 



Numerous dikes cut the syenite massif but have not been traced 



