374 J. BARRELL FLUVIATILE ORIGIN OF OLD RED SANDSTONE 



fine sediment in shallow water, which frequently retired and left wide tracts 

 of muddy shore to be dried and cracked by exposure to the sun" (page 393). 



The resemblance which the fissile calcareous flagstones "bear to some of the 

 so-called fresh-water limestones and cement-stones at the base of the car- 

 boniferous system of the south of Scotland, cannot but strike any one who is 

 familiar with the latter strata. This likeness includes not only the composi- 

 tion, color, and mode of weathering, but even the minute wavy lamination 

 indicative of intermittent but tranquil deposit. Other shaly layers are strongly 

 pyritous" (page 400) . . . "organic remains abound in the strata exposed 

 on the shore between Dunnet Bay and Reay. Fragments of fish and coprolites 

 are scattered abundantly through most of the flagstones. Some of the cal- 

 careous shales are full of Estheria, while traces of plants occur in great num- 

 bers, though generally in a somewhat macerated condition" (page 393). 



The groups to which the plants belong are Ferns, Calamites, Lepidodendrids, 

 Stigmaria, and Araucarioxylon. No traces of marine plants have been found. 



7. Gill's Bay Red Sandstone 400 feet 



This formation consists of red, friable, false-bedded sandstones, both its base 

 and top interleaved with seams of flagstone and grading into the flagstone 

 groups. No fossils have yet been found in these sandstones. 



8. Euna Flagstones 1,000 feet 



To the alternation of red sandstone and flagstones succeeds the Huna flag- 

 stone group having characters similar to those of the Thurso flagstones. 



9. John o'Groat's Red Sandstones and Flagstones 2,000 feet 



These consist of a mass of false-bedded red sandstones, with intercalations 

 of flagstones, the whole much resembling the Gill's Bay formation. The sand- 

 stones "occur in successive thicker zones, between which lie many alternations 

 of red sandstone, red and blue flagstones, grey shale, and impure limestone. 

 These latter strata are quite undistinguishable from portions of the older 

 flagstone groups. The highest part of the group consists of a thick mass of 

 false-bedded red sandstone, without flagstone or shale. Fossils occur in some 

 of the blue flagstones and impure limestones" (page 404). 



Old Red Sandstone of the Orkney Islands. — The greater part of the 

 section previously given is traceable into sandy and conglomeratic facies 

 contiguous to the old margins of the basins. It is important, therefore, 

 in any view of the Orcadie basin as a whole to compare the preceding 

 with the stratigraphic characters as observed throughout the Orkney 

 Islands, since these were much farther from the limits of the basin. 



In the same report from Geikie from which the preceding statements 

 have been abstracted is given also an account of the stratigraphy as 

 observed in the Orkney Islands. 



"Almost the whole of the Orkney islands consist of flagstone and sandstones 

 of the Caithness flag series. The only other formations present appear in the 

 southwestern part of this group. A small ridge of the underlying crystalline 

 rocks rises to the surface at Stromness" (page 408). 



