450 - PROFESSOR GEIKIE ON THE 
Unfortunately, its actual relations to the Old Red Sandstone rocks are everywhere 
obscured. But as it forms a great flat cake, with vertical joints, spreading 
over the edge of the upturned metamorphic beds, and must almost certainly — 
have been intruded between the crystalline platform and an overlying cover of 
rocks, now removed by denudation, the reference of it to the Old Red Sand- 
stone period may be accepted as highly probable. Dykes of a material very 
like or identical with the lavas of Hillswick traverse this pink rock on Ronas 
Voe and Muckle Rooe ; so that it would appear to be at least older than some 
of the igneous rocks of the district. Though the general aspect of the coast 
cliff of the Ronas Voe rock recalls that of the remarkable pink “ porphyry” 
of Papa Stour described at p. 420, the two rocks differ very much in their 
external petrographical and internal microscopical characters. 
An interesting and important discovery made by Messrs Prac and Honxe 
is the occurrence of numerous plants, evidently similar to those of Lerwick, in 
the altered sandstones or quartzites south of Melby. The whole of that district 
would thus appear to consist of Old Red Sandstone which has been much 
metamorphosed and invaded by pink porphyry. 
‘With regard to the fossil lists, I have to add that Dr Traquair has kindly 4 
looked over the Table II. on p. 452, and given me a few additional references, 
He informs me that he has made some progress with the revision of the ichte 
ology of the Old Red Sandstone, and aa considerable changes will requi 
to be made on all published lists. 
: NOS a nd wechrsizdn disk i's Def) 

