PETROLOGY IN AMERICA. 471 



without elaeolite, and this too passes at its margin into 

 porphyritic varieties with fine-textured ground-mass. The 

 special interest of these latter is that they are rhomb- 

 porphyries, reproducing in the peculiar habit of their por- 

 phyritic felspars and in other respects the characteristics of 

 the well-known rocks of the Christiania district. As in 

 other districts of elaeolite-syenites and augite-syenites, there 

 are in the Apache Mountains region numerous dykes of 

 tinguaite and bostonite, and to these two types Osann adds 

 a third, more acid, to which he gives the name paisanite. 

 This contains quartz, and has some resemblance to the 

 grorudite of Brogger, but differs from it in having the soda- 

 amphibole riebeckite instead of segirine. Moreover this 

 mineral occurs not in crystals but in fibrous and irregular 

 patches in the ground-mass, a common character in the 

 soda-bearing amphiboles of the whole group of rocks. The 

 lava-flows of the district, besides basalt and rhyolite, include 

 a type of phonolite which is distinguished by the name 

 apachite. Its special characters are firstly the abundance of 

 amphiboles in addition to augite and segirine, and secondly 

 the prevalence of microperthitic intergrowths in the felspars 

 of the ground-mass. The amphibole minerals are a brown 

 variety, apparently between arfvedsonite and barkevicite, 

 and a blue one resembling that which Brogger has described 

 in his grorudite dykes under the name cataforite. The age 

 of these various eruptive rocks in Western Texas has 

 not been determined further than that they are post- 

 Carboniferous. 



Before leaving the subject of nepheline or elaeolite- 

 syenites, we may note a new Canadian occurrence recently 

 described by Adams (17). It occupies a large area among 

 the Laurentian rocks at Dungannon, Ontario. Nepheline 

 is by far the most abundant constituent, and one variety of 

 the rock is composed almost wholly of this mineral with a 

 little hornblende or mica, thus corresponding with the ijolite 

 of Ramsay and Berghell from Finland. The felspathic 

 constituent of the rock is albite to the exclusion of ortho- 

 clase, as in the occurrence at Litchfield, Maine, which 

 Bayley has styled litchtieldite. The other minerals present 



