166 SCIENCE PROGRESS. 



schists right up to the gneiss. They, however, never 

 enter it. Their complete absence from the '' basal 

 gneisses" is a fact that has long been known to Italian 

 geologists, and has been used as a test point in the 

 separation of the newer and older gneisses ; Gastaldi, 

 indeed, used it as a proof that these "greenstones" could 

 not be igneous, but must be bedded sediments of a type 

 peculiar to the time of the " pietre verdi " series. He says 

 that if they were intrusive they must somewhere have 

 cut the basal gneiss. And it seems impossible to give any 

 other reply to this argument except that the basal gneiss 

 is newer, and not older, than the schists. A final proof is 

 afforded by the fact that the gneiss is remarkably fresh in 

 character, and has not been affected bv the earth-move- 

 ments which have crushed and crumpled the schists around 

 them. It is frequently observed that beds in the centre 

 of a great mass of rock escape alteration, while the margins 

 are crushed and changed. But in the case of these " Wal- 

 densian gneisses " thin veins of aplite are quite fresh and 

 uncrushed, while the rocks they traverse have been rolled 

 out into schists. 



Having thus attempted to show that the gneisses were 

 formed later than the schists, instead of before them, the 

 author endeavours to decide their age. This is a difficult 

 task, and rests on the classification of the earth-movements in 

 the district, and on the age assigned to the "schistes lustres". 

 To take the latter first, the author is unable to express any 

 very positive conclusion upon this subject. He remarks 

 that they "are unquestionably pre-Triassic," and that they 

 are probably Palaeozoic. He rests the former decision on 

 the sections at Mount Genevre, where the schists underlie 

 the basement beds of the Trias. Moreover, there appears 

 to be sufficient evidence elsewhere to show that the schists 

 are pre -Carboniferous. The author knows of no evidence 

 which enables the date to be fixed more definitely than 

 this. They may be of any age before the Carboniferous. 

 His objection to throwing them back into the Archean 

 rests on the recent discovery in these beds of some cleaved 

 radiolarian muds. The fauna in this is very imperfectly 



