372 J. BARRELL FLUVIATILE ORIGIN OP OLD RED SANDSTONE 



Subdivisions of the Lower Old Red Sandstone of Caithness 



Feet 



9. John o'Groat's Sandstone and Flagstone Group 2,000 



8. Huna Flagstone Group 1,000 



7. Gill's Bay Red Sandstones 400 



6. Thurso, or Northern Flagstone Group 5,000 



5. Wick, or Eastern Flagstone Group 5,000 



4. Langwell and Morven Sandstones and Conglomerates 2,000 



3. Badbea Breccia and Conglomerate 300 



2. Braemore and Ousedale Sandstones 450 



1. Basement Conglomerate 50 



16,200 

 The significant details of these formations are as follows : 



1. Coarse Basement Conglomerate 50 feet 



This was laid down on an uneven floor of igneous and metamorphic rock. 



It presents a remarkable granitoid aspect to such an extent that it is often 

 not easy to determine where the conglomerate ends and the granite begins. 

 Its component blocks vary in size up to as much as a yard, or even more, in 

 length. The bowlders are for the most part tolerably well rounded. The thick- 

 ness given was measured at the place where studied, but the basement con- 

 glomerate over the basin as a whole must vary much both in thickness and in 

 age. 



2. Braemore and Ousedale Sandstones 450 feet 



These are dull chocolate-red sandstones with sandy shales or clays. It is 

 noteworthy how abundantly pink orthoclase occurs in the matrix of many of 

 the sandstones. The red shales and sandstones of Braemore are sometimes 

 pitted as if by rainprints, but have as yet yielded no fossils. 



3. Badbea Breccia and Conglomerate 300 feet 



By far the most conspicuous member of the Old Red Sandstone series in the 

 south of Caithness is a remarkable breccia or brecciated conglomerate. It 

 occurs in thick beds, wherein little or no trace of stratification may be found. 

 The stones, considerably smaller than in the basement conglomerate of Brae- 

 more, seldom exceed five or six inches in length. They consist mainly of pink 

 cleavable orthoclase, pink granite, grey quartz-rock, white vein-quartz, and 

 occasional pieces of red sandstone. The feldspar is the predominant ingre- 

 dient, and likewise enters largely, in a comminuted state, into the composition 

 of the paste (pages 37S-379). 



4. Langwell and Morven Sandstones and Conglomerates 2,000 feet 



The Badbea breccias and conglomerate "pass up into a thick series of dull 

 chocolate-red, grey, and yellow sandstones, with layers of dull-red and olive- 

 colored shales and of fine conglomerate. ... In their lower part they are 

 highly felspathic, with a rather coarse texture, and many scattered pebbles, 

 as well as nests and bands of conglomerate. Higher up they are more flaggy, 

 and they finally pass upward imperceptibly into the dull-red and grey flag- 

 stones of Berriedale. Nothing but an arbitrary line can be drawn for their 

 upper limit. . . . The group has as yet yielded no fossils" (pages 379-380). 



