120 Rev. J. Clifton Ward — Geology of the Lake District. 



Chronological Summary. 



Skiddaw Slate Period 



Volcanic Period 



Possible Gap 



Upper Silurian of Lake 



District 



Old Eed Period 



Carboniferous Period 



Post - Carboniferous 

 Periods 



Million 

 of years. 



6 



u 



15 



24 

 62 



Rate of Deposition. 



six in. per annum. 

 To~ in- per annum. 



-rb- in. per annum. 



12,000ft. @ -rViri. per ann. 

 8,500ft. @ -Ay in. „ 



^b- in. per annum. 



Rate of Denudation. 



lft. in 1,000 years. 

 1 ft. in 750 years. 



The above result may, after all, in itself be of little value ; but if 

 it helps to make one realize the respective magnitude of the various 

 operations which the Lake District has undergone in the course of 

 its long history, one main purpose will have been served. Whether 

 the Old Eed Period was one of such duration as here indicated or 

 not, its length, in respect to the other formations, is probably shown 

 with some degree of truth. Whether 60 millions of years have 

 elapsed since the beginning of the Skiddaw Slate Period or not, 

 it is more than likely that the time which elapsed between the first 

 laying of the foundations in the early Skiddaw Slate sea and that 

 time when the roughly-hewn block of country was turned out at 

 the close of the Carboniferous epoch, for the tracing of scenic 

 details upon it, was greater than the time consumed in the actual 

 formation of our present mountain and valley system by subaerial 

 denudation. 



Part III. — Notes on the Possible Subdivisions of the Skiddaw 



Slates. 



Introduction. — In making some observations upon the correlation 

 of the Skiddaw Slates with the Silurian rocks of Wales, I wish to 

 bear in mind the following axioms. (1). Physical evidence, such as 

 character and thickness of deposits, can be taken as no absolute 

 guide in the correlation of distinct groups of strata separated from 

 one another by considerable distances. (2). A general sequence of 

 similar deposits in two distinct but not Avidely separated areas may 

 be held to indicate a succession of similar conditions prevailing at or 

 near the same period of time. (3). The evidence of fossils as to the 

 age of a deposit is generally trustworthy when it is grounded upon 

 assemblages of life, and when corroborating evidence is to be gathered 

 from the formations above and below. (4). In determining the age 

 of a formation due weight should be given to both physical and 

 palseontological evidence, but neither should be relied on exclusively. 



Applying these axioms to the case of the Skiddaw Slates, I wish 

 to see whether the palasontological dictum as to their Lower Llan- 

 deilo or Arenig age can be unhesitatingly supported. 



