600 J. G. Goodchild — Deutozoic Bocks of North Britain. 



are separated from the strata containing Cephalaspis lyelli by one 

 of the most extensive unconformities in the whole geological series. 



It may serve a useful purpose to summarise here, in a tabular 

 form, the foregoing statements regarding the stratigraphical relations 

 of the various Scottish Old Keds, which, accordingly, is as follows : — 



Older Deutozoic Kocks, as developed in Scotland. 



Approximate 

 Upper Old Eed Sandstone. thickness iu feet. 



2. Higher subdivision, or Elgin Beds. 



1. Lower subdivision, or Nairn Beds. 0. — 1,000. 

 [Extensive unconformity .'\ 



Orcadian Old Red, 



5. John o' Groats' Flags. 

 4. Thurso or Rousay Beds. 



3. Achanarras, Stromness, and Cromarty Beds. 



2. Berriedale Sandstones. 



1. Badbea Breccias and Basal Conglomerate. 0. — 16,000. 



Caledonian Old Bed Sandstone. 



3. Strathmore Sandstones (the upper part of 



which may be contemporaneous with the 

 lowest jjart of the Orcadian). 

 'Myriapod Beds. 

 Volcanic liocks. 



Acauthodian Beds of Turin Hill. 

 Cephalaspis Beds of Auchtertyre. 

 Volcanic Bocks. 



PterygotKs Beds of Carmylie, etc. 

 ^Tealing Beds. 

 1. Lower Series of Sandstones, Mudstones, Con- 

 glomerates, etc. ; base not seen. Banging to ? 20,000. 

 [Extensive nnconfor)mty.'\ 



The Lanarkian Bocks (Dowutonians of the Geological 

 Survey, the original Lower Old Red of 

 earlier writers). 

 Ludlow Rocks. 



It will thus be observed that what has been called " The Old Eed 

 Sandstone" in Scotland is by no means a single formation; nor can 

 it be regarded as merely two. On the contrary, it must be obvious 

 from a consideration of the foregoing statements that we are dealing 

 with a succession of formations, which, it seems to me, must col- 

 lectively have required a period of enormous length for their 

 accumulation. This, it will be noted, is evidenced not only by the 

 great thickness of both sedimentary and volcanic rocks accumvUated, 

 but also by the extensive unconformities, and equally so by the 

 numerous and important palgeontological changes which are known 

 to have taken place during the period in question. 



In reflecting upon these facts the chief interest centres upon the 

 formations which are of older date than the Upper Old Red Sand- 

 stone and newer than those of Silurian age. If the remains of so 

 varied and important a set of geological formations can be shown 

 to exist even yet iu Scotland, one is led to enquire whether it may 



