370 J. BARRELL FLUVIATLLE ORIGIN OF OLD RED SANDSTONE 



or the top of the Dunnottar conglomerates. Odd fossils have occasionally been 

 obtained from other horizons, but they are quite a negligible quantity." 25 



To the west, the sections as exhibited in Fife and Kinross show enor- 

 mous quantities of agglomerates, lavas, and tuffs. More or less rude 

 sorting of the breccias shows some rearrangement by water. Some beds 

 of breccia betray, however, no stratification ; others, on the contrary, show 

 a great deal of rounding and sorting of pebbles and boulders. A. Geikie 

 states that the series of deposits in the Caledonian basin everywhere 

 presents traces of shallow-water conditions. 26 He seeks to interpret the 

 whole as laid down in an open lake and sorted by wave action. He notes 

 that — 



"An objection may arise that the remarkable coarseness of the conglomer- 

 ates, and the large size of many of their included bowlders, are suggestive 

 rather of the powerful breakers of the open sea than of the limited wave- 

 action of a lake or inland sea. But possibly the coarseness of the shingle may 

 rather be some indication of the dimensions of the lake and of the power of 

 the waves; along its exposed shores." 2T 



It seems, however, that a reinterpretation is called for. The widely 

 extended and coarse conglomerates do not suggest shore action, but re- 

 semble the stream-borne detritus of Eocky Mountain valleys. Their 

 coarseness, thickness, and distance of transportation are all significant of 

 stream rather than wave action. The red or gray sandstones and red 

 shales are similar to the Catskill deposits of Few York and Pennsylvania, 

 and are such as in India and North America have become commonly 

 regarded as fluviatile in origin. 



MIDDLE OLD RED — ORCADIAN FORMATIONS 



Relations to older rocks. — During the middle part of the Old Red 

 Sandstone period the chief axes of subsidence and deposition were trans- 

 ferred to the northern part of Scotland. Its locus has become known as 

 the Orcadian Lake, or, better, the Orcadian basin. Disturbance and some 

 erosion of the Lower Old Red may have resulted in retransfer of material. 

 The enormous thicknesses of deposits imply vigorous crust movements 

 and profound erosion. The fossiliferous beds show that the Middle Old 

 Red is younger than the Lower Old Red to the south, but there is no 

 doubt but that the Caledonian deposits once extended northwest of the 



23 The Old Red Sandstone of Forfarshire, Upper and Lower. Geol. Mag., Decade 5, 

 vol. v, 1908, pp. 3^-401. 



26 Text-book of geology, 1903, p. 1008: 



27 Geology of East Fife. Mem, of t!je Geol. Survey, Scotland, 1902, p. 43. 



