772 T. G. B0NNEY ON THE SERPENTINE AND 



" This rock appears to coincide in all its properties, both chemical 

 and physical, with the mineral chonicrite, which is stated by Dana 

 (Min. ed. 1868, p. 494) to be found associated with serpentine in 

 Elba. It differs in having less Si and more Fe." 



The commonest rock on the shore near Lendalfoot is serpentine, 

 which, with occasional intervals of sand &c, extends for about one 

 mile to north and two and a quarter to south of that hamlet. Toge- 

 ther with it (according to Dr. Geikie) the " dioritic" rocks appear 

 " interstratified as small lenticular layers. The principal varieties 

 are diorite and hypersthenic" I will retain the term "dioritic" 

 for convenience of reference, excluding the latter variety. 



The "Dioritic" Bocks. 



As in the case of the hornblende schists of Cornwall it was no 

 part of my plan to examine into the lithology of these rocks after I 

 had once settled their relation to the serpentine. Some of them 

 certainly appeared to be metamorphic stratified rocks ; others, how- 

 ever (especially some porphyritic varieties), struck me as having a 

 remarkably igneous aspect, so I collected two or three specimens of 

 these for microscopic examination, thinking they might illustrate 

 extreme metamorphism. I now regret that I did not more minutely 

 observe the details of this series, for I find that these examples are 

 igneous rocks ; they contain very characteristic and well-preserved 

 augite, but no hornblende, and show the usual structure of a dolerite. 

 The following is a brief description of the four specimens which I 

 selected for microscopic examination *. 



(1) Specimen collected from mass about 200 yards north of Lendal- 

 foot cottages (porphyritic in places) contains much well-preserved 

 augite, some viridite (serpentinous variety) probably replacing olivine, 

 and exhibits the general structure of a dolerite, though the plagio- 

 clase has lost its characteristic appearance and is replaced by pseudo- 

 morphous products of a granular to rather fibrous structure, showing 

 bright colours with crossing Nicols. I suspect more than one zeolitic 

 mineral is present, but cannot venture to identify them. 



(2) Specimen from mass included in serpentine about 100 yards 

 south of skerry at back of cottages, Lendalfoot, exhibits a few 

 augite crystals, very well preserved, in a ground-mass composed of 

 small grains of augite and crystals of plagioclase (highly altered, 

 earthy, and semiopaque), together with ferruginous granules. Some 

 of the small grains of augite have a rather fibrous aspect, are iron- 

 stained, and exhibit dichroism. Much of the ferruginous mineral 

 resembles altered ilmenite. It is difficult to speak positively, but 

 I believe this is only an altered dolerite. 



(3) Specimen from a porphyritic variety with large crystals of 

 white plagioclase, south of Lendalfoot (I believe the one mentioned 

 by Mr. Geikie, he. cit. p. 526, as a felstone which " illustrates how 



* I may state that the pectolite which is associated with some of the rocks in 

 this series is a very beautiful microscopic object with crossing Nicols. I think 

 that I noticed in it the optical character which is mentioned by Prof. Dana 

 (' Text-book of Mineralogy,' p. 315). 



