80 



REUSCH, < COSSA, (2 > JULIEN (8 > and others. With regard to these rocks 

 the important question arises : Are they eruptive rocks of later date than the 

 schists or must they be regarded as integral portions of the latter ? The 

 observations of REUSCH and BROGGER on the peridotites of Almeklovdal 

 and other localities in Sondmore (Norway) are especially interesting in 

 relation to this question. Here the rocks consist of perfectly fresh olivine, 

 green hornblende (smaragdite), chrome-iron ore and a few grains of brownish 

 yellow enstatite. They possess a marked schistosity, recognisable in hand 

 specimens, and also a banding due to variation in the relative proportions of 

 the different constituents. Some of the bands consist almost entirely of 

 olivine ; others contain a large amount of smaragdite. The banding and 

 schistosity are strictly parallel to each other and to the corresponding features 

 in the surrounding gneissic series. These observations appear to prove 

 conclusively that the rocks in question must be regarded as integral portions 

 of the crystalline schists. They do not of course disprove the igneous 

 origin of the peridotite, for it is now becoming evident that the crystalline 

 schists are largely composed of igneous material. 



In 1876 DATHE described a number of olivine rocks and serpentines 

 from the granulitic region of Saxony. He divided the unaltered peridotites 

 into two groups : gamet-olivine rocks and awtrrfifp-otirinr rocks. For the latter 

 group WADSWOBTH has subsequently proposed the term Sajconite. 



In 1869 Professor TSCHERMAK (4) called attention to the existence of an 

 olivine-rock which is intrusive in the Neocomian formations of Moravia and 

 Silesia, and proposed for it the name of Picrite. This rock is of a dark green 

 colour and either distinctly or finely crystalline. Olivine forms about one- 

 half of the entire mass, and sometimes occurs in fairly large crystals thus 

 giving the rock a porphyritic aspect. The groundmass contains hornblende, 

 diallage and biotite, but the relative proportions of these constituents varies 

 in different specimens. Magnetite is always and calcite often present. A 

 little glass may sometimes be observed. In his definition of the term 

 TSCHERMAK lays special stress on the fact that about half the rock is 

 composed of olivine. 



In 1874 Professor G UMBEL (5) described a rock of similar composition, 

 occurring in the lower palaeozoic strata of the Fichtelgebirge under the name 

 of Palaeopicrite. This rock was observed by him in no less than twenty 

 localities. It is described as closely resembling a dark coloured diabase in 

 appearance, and as consisting very largely of olivine ; together with enstatite, 

 chrome-diopside, augite and magnetite. Rocks of the same type are found 

 associated with the Devono-carboniferous strata of Nassau.' 6) 



(1) Das Grundgebirge im siidlichen Sondmore. Kristiania, 1877 : and also N.J. (Ref.), 

 1880, Band II., p. 194. 



(2) Ricerche chim. e. Microsc. &c. Turin, 1881 ; and N.J. (Ref.), 1882, Band II., p. 47. 



(3) Proc. Boston Soc. Nat. Hist., XXIL, 1882, p. 141. 



(4) Die Porphyrgesteine Oesterreichs. Wien. 18G9, p. 239. 



(5) Die paliiolithischen Eruptivgesteine des Fiehteltrebirges. Miinchen, 1874. 



(6) OEBBEKE. Ein Beitrag zur Kenntniss des Palaeopikrits. Inaug. Diss. Wiir/burg, 

 1877. 



