194 PKOCEEDIN'&S OF THE GEOLOGICAL SOCLETT. [Jan. 8, 



determined ; but among them my friend Mr. Joass, who possesses 

 such an intimate acquaintance with the Scottish Old Red Sandstone 

 and its fossils, was able to detect the remains of Osteolepis and Gy- 

 roptychius. 



(g) Origin. — That the great masses of flagstone so abundant in 

 the " brecciated beds " were derived from the Middle Old Red Sand- 

 stone or Caithness Flags is thus demonstrated both by their 

 mineral characters and their included fossils. There is every reason 

 to believe that the associated blocks of sandstone and indurated 

 shale came from the same source ; indeed, as we have seen, they are 

 found interstratified with the flagstones in some of the great 

 transported masses. We are thus led to conclude that by far the 

 greater number, if not the whole, of these transported blocks were 

 derived from the Caithness Flagstones or Middle Old Red series, the 

 difficulty suggested by Sir Roderick Murchison disappearing, as we 

 have already seen, now that we have demonstrated the enormous 

 faulting and removal of beds by denudation which have taken place 

 in this district subsequent to the deposition of the Jurassic series. 

 The absence of an admixture of foreign blocks from widely different 

 and distant formations is another feature in which the " brecciated 

 beds " differ from those of more modern date, which we now know 

 to have been due to the causes which operated during the Glacial 

 epoch. 



§ 5. General Conclusions as to the Conditions under which the 

 " Brecciated beds " were deposited. 



Refraining, for the reasons already stated, from attempting at the 

 present time to frame any complete theory to account for the for- 

 mation of these singular beds, I believe we are nevertheless justified, 

 from the consideration of the foregoing facts, in accepting the follow- 

 ing general conclusions concerning them : — 



1. The whole Jurassic series of Sutherland was deposited in close 

 proximity to land, and large portions of it actually within the es- 

 tuaries of great rivers. This is as true of the beds of the Upper 

 Oolite as of the other portions of the Jurassic system. 



2. The land which bordered the Jurassic sea was not composed 

 of the granites, gneisses, and Old Red conglomerates, which at pre- 

 sent constitute so large a portion of Sutherland, but of the cal- 

 careous flagstones and associated strata under which the former 

 strata were once deeply buried in this country, and which still form 

 the surface of so large a part of the adjoining county of Caithness. 



3. The numerous marine fossils of the Upper Oolites of Suther- 

 land leave no room for doubt that they were accumulated in the 

 sea ; but the genera of Mollusca which are most abundant in their 

 fauna, the mineral characters, and the nature of their rock-structure 

 make it equally clear that they were accumulated under decidedly 

 littoral conditions. 



4. The large and exquisitely preserved flora of these beds indi- 

 cates that rivers, laden with the spoils of the land, added large and 

 constant contributions to the formation of these same beds. 



