W. N. Benson — Origin of Serpentine. 695 



Von Buch, De la Beche, Brongniart, De Beaumont and 

 others claimed it was of igneous origin, being followed in 

 this by Whitney and Rogers in America. Some authors, 

 like Macculloch, considered it possible that serpentine 

 might originate both from igneous or sedimentary 

 processes (for literature see Hunt, 1883). De la Beche 

 was particularly clear in his recognition of the intrusive 

 origin of the serpentines, and stated with regard to those 

 of Liguria, that they were "thrust into the Oolitic rocks, 

 but not into the supra-Cretaceous. The intrusion is con- 

 nected with earth-movements ' ' (De la Beche 1831). 

 He also claimed an igneous origin for the British serpen- 

 tines. Haidinger (1823) held that the famous Snarum 

 serpentine crystals were primary, but Breithaupt (1831) 

 suggested that they were pseudomorphs after olivine, 

 and intimated that augite and hornblende might be sim- 

 ilarly changed. After twenty years of discussion this 

 conclusion was accepted as the result of Rose's work 

 (1851). 



Meanwhile the views of Rose and Bischoff (1854), as to 

 the possibility of the metasomatic replacement of rocks 

 by material introduced by percolating solutions, led to 

 wide speculation. Almost any rock, it was assumed, 

 could be transmuted into serpentine; the apparently 

 gradual passage of a differentiated massif from granite 

 into serpentinized peridotite was considered evidence of 

 such a replacement. The necessary check to hypotheses 

 of this character was given by the work of Sandberger 

 1865-71) and Tschermak (1867), the way for which 

 had been suddenly opened by the discovery of the 

 lherzolites of the Pyrenees by Des Cloiseaux (1862) and 

 Damour (1862), of the dunite of New Zealand by Hoch- 

 stetter (1864), of the Scandinavian olivine-rocks by Kjer- 

 ulf (1864), and of various Alpine peridotites. Sandber- 

 ger showed that varying amounts of residual olivine and 

 bronzite occurred in the serpentines of Saxony ; Tscher- 

 mak, the first to employ microscopical methods of inves- 

 tigation, corroborated this, tracing the alteration of the 

 olivine into serpentine, and describing the typical mesh- 

 structure produced. He showed that the apparent 

 passage of serpentine into aluminous gabbros and 

 eclogites was due to an original heterogeneity of the rock- 

 mass ; the gabbros and eclogites do not become serpen- 

 tine, but only the peridotites with which they are 

 intimately associated. 



