1892.] Mineralogy and Petrography. 511 



magma than the feldspar fragments. They are consequently often 

 entirely dissolved, leaving behind them scarcely a trace of their former 

 existence. When cores of these remain they are surrounded by mag- 

 netite, quartz (?) and sometimes newly formed biotite. Before closing 

 his article the author calls attention to the differences in the action of 

 diabasic and basaltic magmas upon enclosed fragments, the most 

 noticeable being that in the former case no glass inclusions are devel- 

 oped in the material of the enclosed substances, while in the latter 

 case these are abundantly formed. 



The Basalts of Cassel.— Among the basaltic rocks occurring 

 in the neighborhood of Cassel, Fromm 1 distinguishes limburgites, 

 basalts and nepheline-basalts. All are porphyritic, with olivine, augite 

 and labradorite (in the plagioclastic varieties) as phenocrysts in a 

 groundmass of augite, plagioclase, probably sanidine, magnetite, 

 ilmenite, hematite, mica and apatite in the feldspathic rocks and in 

 the nepheline basalts with a groundmass of much the same character 

 except that nepheline replaces the feldspar. Besides, a little glassy 

 base is always present. Some of the olivine is brecciated as if broken 

 by the movement of the rock in which it occurs. Again it is corroded, 

 when it is often surrounded by a rim of glass, which the author 

 thinks is due to rapid cooling of the dissolved portion of the mineral. 

 The augites are often zonal, with the deeply colored zones within in 

 the plagioclase basalts, and in the nepheline varieties with the lighter 

 colored zones in the interior. The nepheline present in the nepheline 

 basalts is either in the form of a uniformly distributed groundmass in 

 which are imbedded microlites of augite or in little nests between the 

 other minerals, or finally as small areas with crystal cross sections. 

 Mellilite was detected in a nepheline basalt and good plates of pleo- 

 chroic ilmenite were observed in several plagioclase basalts. Glass 

 was present in the limburgite, in several plagioclase basalts and in one 

 nephelinic variety. Quartz fragments included in the | 

 basalts are surrounded by rims of augite crystals, between which and 

 the nucleus is often a zone of glass. Sometimes the quartz has entirely 

 disappeared, leaving only glass encircled by a crown of augite. Analy- 

 ses of all the varieties of the rocks studied accompany the paper. 



The Rocks of the Piedmont Plateau.— In an excellent arti- 

 cle on the structure of the Piedmont Plateau in Maryland, G. H. 

 Williams 2 divides the region between the Catoctin Mountains and the 



l Zeits. d. d. Geol. Ges. xliii, p. 43. 



