396 MK JOHN S. FLETT ON 



(Birsay and Evic) will, in my opinion, be found the most suitable for this purpose. If 

 we take a section from Crustan Point in Birsay, the centre of the West Mainland anti- 

 cline, to Burgar in Evie, where we cannot be far from the level of those beds which in 

 the west of Rousay contain Thursius pholidotus (Traq.) and Coccosteus minor (Miller), 

 and strike southwards across the narrow Eynhallow Sound, the total distance is five 

 miles, measured across the strike of the beds. The dips throughout are eastwards, and 

 their average amount is about 3°. There is no evidence of any important fault. The 

 thickness must in consequence be about 1300 feet. The exact position of the Crustan 

 beds in the Stromness series is difficult to fix, but, as along the western shore from 

 Skaill Bay by Outshore Point to the Brough of Birsay, the dips are mostly N.W., as 

 we travel northwards the section is a constantly ascending one, and the beds which 

 occupy the centre of the anticline at the northern shore must be far higher in the series 

 than those which occupy a similar position in the neighbourhood of the Harray Loch. 

 The Crustan beds in consequence are, in all probability, on a similar level to those in 

 the vicinity of Skaill Bay ; and if we add the lower half of the thickness between 

 Crustan and Burgar to that from Tenston to Skaill, we obtain a total thickness of about 

 2500 feet for the Stromness beds of Orkney. The beds of Evie may, on the other 

 hand, be relegated to the basal part of the Rousay series, and as yet there is no palajon- 

 tological evidence to prevent such a step. These passage beds, in fact, between the 

 Stromness and Birsay series below, and the Rousay beds above, are comparatively 

 unfossiliferous, and have yielded little of value to the most careful search. 



Mainland 



Sect. 1.— From Skaill Head (Sandwick) to Start Point (Sanday). 



II. The Rousay Beds. 



The Rousay beds of Orkney lie mostly to the north and east of the county, where 

 they cover a much more extensive area than the better known Stromness series. As 

 yet, however, little attention has been paid to them and their fossil contents, and the 

 scarcity and imperfect state of their fossils is indeed disappointing to one who has been 

 accustomed to investigate the West Mainland beds. One may travel for days along 

 the shores or among the quarries on this group of rocks without bringing home more 

 than one or two imperfect specimens. Yet they are never entirely barren, and careful 

 search is always rewarded with recognisable organic remains, usually scattered bones and 

 scales, while in a few places we may find even entire fishes, as perfect in every detail as 

 those which abound in certain of the quarries of Sandwick and Stromness. Very 

 characteristic of these rocks are the scattered bones, the teeth, and sculptured scales of 



