acai.|mv o F sci-nces] NORTHERN EUROPE. 19 



Silurian rocks, followed, usually after a break of varying importance, by Devonian and lower 

 Carboniferous rocks, all very disturbed and mucb metamorphosed in the neighborhood of the 

 crystalline massifs. Lepsius ('87-' 10), Gabert ('07), Dull ('02), Zeigler ('14), and others consider 

 that much of the gneiss of these crystalline areas may be profoundly metamorphosed Palaeozoic 

 rocks. Lepsius sees in the ampliibolites, eclogites, and serpentines of the gneissic series, or the 

 gabbros with the granulites, the metamorphosed equivalents of the Devonian diabases and 

 picrites, a view with which their petrographic character seems hardly to accord 8 as Uhlig ('07) 

 has shown. On the other hand Credner, Sauer ('03), and others affirm the pre-Cambrian age 

 of the crystalline series. Hence most of the occurrences of basic and ultrabasic rocks such as 

 the serpentine in the schists at the Rauenthal, in the Vosges, that in the gneiss at Zoblitz, and 

 the gabbro of Penig both in Saxony, or the serpentine and gabbro of Miinchberg in northeastern 

 Bavaria, can not be discussed from our tectonico-petrographic standpoint. 



In the crystalline foundation of Bohemia the basic and ultra-bassic rocks form numerous 

 lenticular masses, the elongation of which is generally independent of the structure planes of 

 the invaded rock, though locally they may accord with the schistosity. They generally consist 

 of eclogite, garnet-amphibolite, or serpentine. Bergt ('03) has claimed a Carboniferous age for 

 some of these, and Hinterlechner and von John ('09) have thought a similar age to be not impos- 

 sible for certain gabbroid masses with peridotites and diabase intruding into gneisses and 

 granites. They seem to be certainly post-Silurian. A frequent location of serpentine is lying 

 between granulite or gneiss. Near Krems serpentine and granulite alternate in sharply distinct 

 bands (F. E. Suess '03 ; Becke '13) . 



In northwestern Germany the tectonic history is less obscured. Here and there appear 

 fine-grained and cherty Silurian rocks deposited during steady geosynclinal subsidence, which 

 had commenced with the formation of Cambrian conglomerates. The diabasic intrusions in 

 these have a slightly alkaline character. Those in the Bruckberg-Acker series of cherty rocks 

 in the Harz region are analcitic diabase, and alkaline hornblende-proterobases with more or less 

 biotite (Erdmannsdoerfer '08). They seem to be intermediate in character between teschenitic 

 and spilitic rocks. The diabases and porphyrites hi the Lower Silurian rocks of Bolkenhaim 

 in Silesia probably i-epresent a further example. They are more or less schistose, and glauco- 

 phane has developed, replacing an original mantle of alkali-pyroxene about the normal augite. 

 They are associated with keratophyres (Finckh '13). 



The greatest development of basic igneous rocks is that which occurs in the Devonian 

 series, and these are grouped by Steinmann ('05, p. 61) among the ophiolites, though, as will be 

 seen, they are not exactly the equivalent of our alpine type of development. Two zones may be 

 recognized, that stretching from the Rhine, to the Harz Mountains and that in the Fichtelgebirge 

 running from northeastern Bavaria (Hof ) into Saxony (Plauen) . In the first the igneous rocks 

 consists of sills, flows, and tuffs, of spilitic, diabasic, essexitic, and keratophyric rocks, with 

 some picrites, interstratified with a series of geosynclinal sediments, which lie unconformably 

 on the Silurian beds. The sequence commences with the Lower Devonian (Coblenzian) sand- 

 stones, above which comes the Wissenbach slates, containing the earliest of these igneous rocks. 

 The Middle Devonian period was occupied by the deposition of slates, cherts, and limestones, in 

 which time the development of massive and fragmental igneous rocks reached its maximum, the 

 rocks developed being in part alkaline in character. Continued subsidence during Upper 

 Devonian times was marked by the development of clay slates more or less calcareous with 

 impersistent cherts, probably radiolarian (Meyer '09). The accompanying diabasic submarine 

 lavas with pillow-structure are without any noteworthy alkaline features. The Carboniferous 

 period saw the formation of radiolarian cherts, followed by clay slates, which rapidly pass up 

 into the conglomerates, indicating the commencement of the Variscan folding. 



The p'etrographical character of these igneous rocks has been studied in much detail by 

 Brauns and his students, Doermer, Heincck, Reuning, and Rinne. The general summary of 



e The writer has collected and examined a number of these rocks. They seem very different from the indubitable examples of altered 

 Devonian basic eruptive rocks recorded by Beck ('03), though certainly the pressures suffered by the latter would not have been so great 

 as required by Lepsius' view of the origin of the rocks in question. 



