784 T. G, B0NNEY ON THE SERPENTINE AND 



that it can hardly be called a gabbro, the second much resembling 

 the later gabbro of the Lizard, Cornwall*. 



3. That the porphyrites of Balcreuchan and Pinbain Hill are 

 true igneous rocks, and very probably remnants of lava-flows asso- 

 ciated with tuffs or agglomerates. 



4. That several of the rocks into which the serpentine is intrusive 

 are also igneous, and are augitic, not hornblendic. 



5. That there are some doleritic and basaltic dykes of later date 

 than all the above. 



6. That Dr. Geikie's conclusions as to the non-igneous character 

 of the rocks of this district are, so far as regards all the above named,- 

 unsupported by either stratigraphical, penological, or lithological 

 evidence, the proofs of intrusion being remarkably clear and in- 

 dubitable, so that this district must be removed from the list of those 

 which have been supposed to favour the theory of the production of 

 pseudo-igneous from stratified rocks by selective metamorphism. 



The fact of intrusive serpentine, of gabbros of two ages, and later 

 basalt dykes being here associated together, as in the vicinity of 

 Coverack Cove, Cornwall, is a little remarkable. 



As for the date of the above rocks, these last-named basalts are 

 probably Miocene ; the porphyrites (with which I connect those of 

 Knockdolian Hill) are probably outliers of one or more great lava 

 sheets, and no doubt, like others in that part of Scotland, of Old 

 Red Sandstone (probably Middle) age. 



The group of rocks into which the serpentine is intruded, speaking 

 in general terms, is described by Sir E, Murchison as of " Lower 

 Silurian age, Bala, or even Lower Llandovery" (' Siluria,' p. 155 f). 

 Hence the serpentine is later than this epoch, and, as I have shown, 

 almost certainly later than the porphyrite tuffs. The serpentine 

 dyke described by Sir C. Lyell X is intrusive in the Lower Old Red 

 Sandstone of Forfar, and so may possibly form one of a series with 

 those described above. The diallage rock and gabbro north of 

 Lendalfoot must be yet more recent than the serpentine, still all are 

 probably Palaeozoic. 



Discussion. 



Mr. WaeinGtoN W. Smyth remarked on the extraordinary re- 

 semblance of the rocks of Ayrshire to those of the Lizard district, 

 and pointed out that this confirmed the views insisted upon on che- 

 mical grounds by the late Mr. David Porbes. 



* See Quart. Journ. GeoL Soc. vol. xxxiii. p. 895 et seq. 



t See also Quart. Journ. Geol. Soc. vol. vii. p. 137. 



| Edin. Journ. Sc. vol. iii. p. 112. By the kindness of Professor Judd I have 

 had. an opportunity of examining this serpentine, and have no doubt it is an 

 altered olivine-enstatite rock. I have also examined, by favour of Mr. Grieve 

 (Burntisland) and Mr. Hawkins Johnson, F.G.S., some serpentines from Portsoy 

 (Banff), and find them to be generally similar to those which I have been 

 describing in this paper, except that I have often not been able to establish the 

 presence of enstatite, though in some a rather minute pyroxenic constituent is 

 abundant. 



