LETTERS TO A. GEIKIE 



began at an earlier date. After his return they ex- 

 changed frequent letters, chiefly upon technical points 

 suggested by Dana's study of the Taconic rocks and 

 partly by Dr. Sterry-Hunt's publications. Through Sir 

 Archibald Geikie, communications were made to the 

 Geological Society of London. He has kindly shown me 

 all this correspondence, a part of which was confidential, 

 and in making a selection, it is difficult to decide between 

 the interests of the general reader, for whom this memoir 

 is prepared, and those of professional geologists. One may 

 think that too few of Dana's letters are given ; another 

 will find too many. 



DANA TO GEIKIE 



44 NEW HAVEN, October 18, 1873. 



" May I ask you one question on the geology of the 

 Isle of Skye ? Macculloch describes a rock, which he 

 pronounces eruptive and also chrysolite, as occurring on 

 that island, and I have supposed that he referred to a 

 rock related to that of Staffa in being a dolerite. What 

 I desire to know is whether there is any 'Azoic ' or 

 ' Laurentian ' granitoid (that is, precambrian) rock on 

 the island which is chrysolitic, and is strictly a chrysolitic 

 hypersthenite, related therefore to a rock found at Elf- 

 dalen in Sweden and described by Rose. A word from 

 you on this point would greatly oblige me." 



DANA TO GEIKIE 



"NEW HAVEN, January 12, 1874. 



" I was exceedingly glad to have your opinion about 

 the chrysolite of Skye. Prof. T. Sterry-Hunt has re- 

 cently stated that he had examined the collections of 

 Macculloch, and had ascertained that his chrysolite was 

 in the hypersthene rock of Skye. Should you at any time 

 refer to those collections I should be much pleased to 

 learn further your opinion on the subject. 



" I have read your memoirs, which you kindly ad- 

 dressed to me, with great pleasure. You show that Scot- 

 land was an extraordinary region of igneous rocks, almost 



333 



