698 W. N. Benson — Origin of Serpentine. 



development of serpentine, Upper Eocene, Upper Trias, 

 and Paleozoic or pre-Paleozoic, and a general discussion 

 was held on the problem, at the meeting of the Interna- 

 tional Geological Congress in Bologna in 1881. The pro- 

 ceedings are recorded by Hunt, who presided (1883, pars. 

 40-73), and in the first volume of the bulletins of the 

 Italian Geological Society. Novarese's work (1895) 

 marks the acceptance by the Italian Geological Survey of 

 the modern ideas concerning the nature of serpentine and 

 the associated basic rocks, which had thus been foreshad- 

 owed by English workers. 



It was about this time that the Spanish serpentines 

 were first recognized as being derived from peridotites 

 (Macpherson 1875). 



While this discussion was in progress in Europe, there 

 were similar differences of opinion in America. The 

 derivation of serpentine was referred to the alteration of 

 olivine-sands (Raymond and King 1878, Julien 1882, Les- 

 ley 1883), of volcanic agglomerate or diabase (Selwyn 

 1883), of hydromica-schist (Fraser 1883) or the metaso- 

 matic replacement of sandstone (Becker 1888), though 

 in each of the localities described, the intrusive character 

 of the serpentine has since been ascertained, by Lawson, 

 Fairbanks, Lindgren, Ransome, Turner, Branner, Bas- 

 com, Pratt, Lewis or others. Some authors (e. g. 

 Emmons 1855) like Macculloch held that serpentine could 

 be either interstratified or intrusive, but Whitney (1851) 

 and Rogers (1858) recognized them as intrusive, and 

 were followed by others who declared the serpentines to 

 be altered intrusive peridotites. Among these were Kerr, 

 Smith, Genth (1875), Low (1883), Wadsworth (1884), 

 Williams, Diller (1886), and Chester (1887), whose views 

 were the orthodox teaching of their day, and have been 

 generally accepted ever since. The American literature 

 has been summarized by Pratt and Lewis (1905) and a 

 full bibliography will be found in their valuable work. 



The commencement of the last decade of the nineteenth 

 century saw firmly established the recognition of the 

 derivation of serpentine from intrusive peridotite, and 

 we may add that this -perplexing rarity of dikes formed 

 of serpentine or peridotite, and the apparent interbed- 

 ding of these rocks with those among which they occur, 

 is an instance of those peculiar features attending the 

 intrusion of ultrabasic rocks, that have been summarized 



