J. W. JTTDD ON THE SECONDARY ROCKS OF SCOTLAND. (67 



hereafter be proved to belong to the period between the Cretaceous 

 and the Eocene, to the latter formation itself, or even to the 

 Miocene. 



With regard to the underlying beds no such doubt, fortunately, 

 exists. We have clearly marine representatives of the Chalk with 

 Belemnitella mucronata, Schloth., and of the Cenomanian or Upper 

 Greensand ; and the variable estuarine strata between these two 

 marine series must be referred to the whole or to some part of the 

 period represented in other areas by the Lower or Middle Chalk. 



The existence of strata of littoral and estuarine origin, inter- 

 calated in the Upper- Cretaceous series in Bohemia and other parts 

 of Eastern Europe, is a well-known fact. On the other hand, the 

 recent researches carried on with so much perseverance by the 

 United-States geologists in the western district of the North-Ame- 

 rican continent have rendered us familiar with thick formations of 

 freshwater and terrestrial strata representing the same Upper-Cre- 

 taceous period, and also the interval between it and the Tertiary. 

 Under these circumstances the discovery of these Scottish littoral 

 and estuarine deposits is of very great interest — enabling us, as it 

 does, to define a portion of the northern limits of the Cretaceous 

 ocean. The bearing of these facts will be more fully discussed in 

 the fourth and concluding part of this memoir. 



VI. Conclusion. 



Although, as I have before stated, it has been thought advisable 

 to postpone the discussion of the numerous problems of interest 

 which suggest themselves to the student of the remarkable relics of 

 the Secondary rocks in the Scottish Highlands, until the fourth and 

 concluding portion of this memoir is published — yet there are several 

 questions which at the present time engage the minds of geologists 

 upon which, as it appears to me, the facts and arguments of the 

 present part of this memoir have an important bearing ; and these it 

 may not be undesirable to notice briefly at the present stage of the 

 inquiry. Other and more general discussions will be allowed to 

 stand over till such time as I have made the proposed comparison 

 between the characters and modes of preservation of the beds under 

 consideration and those of their equivalents in Ireland, England, 

 Scandinavia, and other portions of the Continent. 



I may briefly point out in the first place the great interest which 

 attaches to the fact that there exists in the north-western part of 

 the British archipelago a series of strata of Cretaceous age exhi- 

 biting evidence of the prevalence of estuarine alternating with 

 marine conditions. The great and deserved amount of attention 

 which is now directed to the similar beds, developed on such a grand 

 scale in Western America, renders the discovery of the minute Scot- 

 tish representatives of the period particularly important at the pre- 

 sent time. It is tantalizing, however, to the British geologist to have 

 to confess that, while he can demonstrate the undoubted fact of the 

 existence of such strata, yet he is obliged to abandon almost all 



3 c 2. 



