392 MR JOHN S. FLETT ON 



at the Point of Inganess. Both have been frequently described, and of the latter 

 locality Professor Heddle has given a map. The granite conglomerate is also seen at 

 the Point of Ness, aud in the flag quarry at Garson Burn on the Kirkwall road. In no 

 case is it of any considerable thickness, 30 feet being probably the greatest depth any- 

 where exposed. With it are mixed sandy flags and coarse arkoses, but it is not a little 

 remarkable how soon it gives place to a normal fine-grained dark grey flag, exactly 

 similar to those which cover such wide districts of the county. In fact, such flags are 

 in many places interbedded with layers of a coarse conglomerate. At Yeskenaby, near 

 Inganess, occurs a series of beds of a coarse sandy millstone grit, in which there is a 

 well known quarry for millstones ; and though its junction with the granite and con- 

 glomerate of Inganess is by means of a small fault, it is easy to see that it is really the 

 rock just overlying the conglomerate let down by this fault against the granite. In 

 fact, on the north-west corner of Inganess, similar beds occur in the cliff where they 

 rest on the granite and granite conglomerate, which form the low shore below. This 

 is in Orkney the only representative of the thick sandstones which elsewhere rest on the 

 basal conglomerate, a fact which strongly supports Sir A. Geikie's opinion that the 

 granite axis of Stromness is a mere local base. Yet the shores on which these fine flags 

 were laid down must have been tranquil and tideless, as deposits so fine could not 

 possibly rest on an exposed or tide-swept shore. The innumerable sun-cracked and 

 ripple-marked surfaces everywhere present in the Orkney flags show that they are the 

 accumulations of a "shallow sea, yet they can hardly be regarded as littoral deposits; 

 they w T ere rather the finer sediment of landlocked areas of fresh water, in which the 

 coarser material rapidly sank to the bottom, and was deposited immediately around the 

 river mouths. 



The Stromness flags. — The flagstones of the Stromness series encircle this granite 

 and conglomerate, and are beautifully exposed in the magnificent sections of the west 

 coast of the Mainland of Orkney, from the Ness of Stromness to the Brough of Birsay. 

 This most interesting coast has been described by almost every writer on the geology 

 of Orkney. Many of the well known localities for Orcadian fossils occur along this shore 

 {e.g., Rocket House, Breckness, Belyacroo, Ramnageo, Quoyloo). Starting from Strom- 

 ness we find the rocks have a westerly dip along the shore to Breckness, W.S.W., then 

 along the Black Craig, W.S.W., at Yeskenaby, W.N.W., at Skaill, W. and N.W., and, 

 north of Skaill Bay along Outshore Point to Marwick Head and the Brough of Birsay, 

 about N.W. for almost the whole way. The dips roll somewhat, being S.W., W., and 

 N.W., as is best seen between Inganess and Skaill Bay, but everywhere there is a per- 

 sistent westerly component. Here we are, in fact, on the west side of a great anticline, 

 which forms the chief structural feature of the West Mainland of Orkney. For about 

 four miles back from the cliff, in all the quarries and burns of Stromness, Sandwick, and 

 Birsay, there is the same universal westward dip. The anticlinal axis runs approximately 

 from Waulkmill Bay in the south to Crustan Point, a mile west of the Brough of Birsay, 

 for to the east of this line, in Firth, Harray, and Evie, easterly dips are consistently 



