GEOLOGY, 327 



NaumaDn to be of Paleozoic age, which is found to be continuous with 

 the other gneisses. 



Marr has lately noticed the crystalline rocks which underlie the 

 Cambrian strata in Bohemia, and has compared the older or basal se- 

 ries of gneisses with limestones to the Dimetran of Wales (Laurentian). 

 They are succeeded unconformably by a newer crystalline series of green- 

 ish schists, with conglomerates, &c., which, according to him, resemble 

 the Pebidian of Wales (Hnronian). These constitute the stage A of 

 Barraude, and are succeeded, after a stratigraphical break, by fossilif- 

 erous Cambrian and Silurian rocks. 



The crystalline rocks of the Taunus were regarded by Dumont as 

 altered Devonian, a view also defended by Lessen, but Gosselet and 

 Koch have shown on stratigraphical grounds that they must be older, and 

 are, in part at least, Huronian. Hunt had already examined the con- 

 tinuation of these rocks in the Ardennes, which, from their association 

 with Oldhamia, must be at least at the base of the Cambrian, and had 

 compared them with Huronian. The question of the develoi^ment of 

 crystalline minerals in sedimentary rocks will be discussed elsewhere. 



Yon Eichthofen has examined the crystalline rocks of northern 

 China, where they occupy a great area, and are divided by him into two 

 groups, which he compares with Laurentian and Huronian, respectively. 

 The first of these is again subdivided into two parts ; the older is a 

 gneiss, often granulitic, with steep dips and a prevailing northwest 

 strike. Eesting unconformably upon it are newer gneissic rocks, some- 

 times hornblendic and chloritic. Both of these Eichthofen would refer 

 to the Laurentian. Eeposing in discordance upon these is a third divis- 

 ion, described as a series of green schists with micaceous and horn- 

 blendic beds, quartzites, and crystalline limestones, jjresentiug many 

 variations in different districts, but regarded by Eichthofen as the 

 probable equivalents of the Huronian, and having a thickness of at 

 least 10,000 feet. These crystalline strata, after having been folded, 

 faulted, and penetrated by intrusive rocks, were subjected to great 

 erosion before the deposition of the succeeding series, called by Eicht- 

 hofen Sinisian, to be noticed below. With reference to the twofold 

 division of the Chinese gneisses, it will remain for further studies to 

 determine whether we have here the representative of two great divis- 

 ions of the Laurentian, and whether we have also to do with newer 

 gneisses, which occasionally, in the Alps, as in parts of North America, 

 xest directly on the pre-Huronian gneisses. 



The rocks to which Eichthofen has given the name of the Sinisian 

 system are developed with similar characters over wide areas, and have 

 an aggregate thickness of from 12,000 to 20,000 feet. They are de- 

 scribed as consisting of three groups in concordant succession : A lower 

 ■one of reddish sandstones and quartzose breccia, a middle group of 

 limestones, sandstones, and argillites, and an upper of limestones, in 



