115 



(1) The true serpentines of the district of Erbeiidorf are due to the 



alteration of a rock composed of olivine and an aluminous 

 grammatite : which rock does not appear to have been con- 

 nected by transitions with the crystalline schists. 



(2) Bronzite, in certain places, enters into the composition of the 



serpentine. 



(3) The alumina of the grammatite has given rise to the formation 



of chlorite. 



(4) Grammatite occurs also as a secondary product. (1) 



(5) In addition to the true serpentines there occur also others 



belonging to DRASCHE'S group of " serpentiiiahnliche 

 Gesteine." 



(6) These latter rocks pass over into true serpentines (i.e. into rocks 



yielding a serpentine-analysis,) with a scaly structure. 



(7) Both varieties of the serpentine from Erbeiidorf contain a 



magnetic iron ore which gives a strong chromium reaction in 

 the borax-bead. 



It will be understood that in the preceding historical sketch we have 

 referred only to some of those papers which have exercised a marked influence 

 on the development of the opinions now generally held on the serpentine 

 question. Many papers of great local importance have of necessity been 

 passed over. Considerable prominence has been given to the later papers 

 because the recent improvements in petrographical methods have enabled 

 students to solve many problems that the old masters of our science could 

 not attack with any reasonable prospect of success. We may sum up the 

 more important points which appear to be definitely established, by saying 

 that three definite types of structure of genetic importance are IIOAV recognised. 



(1) Serpentine with " mascheii-structur " or olivine-serpentine. 



(2) Serpentine with lattice- structure (Gitter- or Fenster-structur) or 



hornblende-serpentine. 



(3) Serpentine with netting-like structure (gestrickte-structur) or 



augite- (aiitigorite-) serpentine. 



BRITISH SERPENTINES. 



It is to Professor BoNNEYthat we are principally indebted for our knowledge 

 of the true character of many British serpentines. He has investigated the 

 field relations and microscopic characters of the rocks of this class as they 



(1) This agrees with BECKE'S observation on " Pilite." WEIGAND'S researches prove that 

 serpentine may be produced by the alteration of grammatite (colourless hornblende) ; BKCKE'S 

 researches show that a similar mineral may arise as a secondary product in connection with the 

 formation of serpentine. 



