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



About the Carboniferous and Upper Silurian x we know sufficient 

 to be sure of tbeir age as compared with the corresponding rocks of 

 other areas ; but it is doubtful whether we are right in assigning, 

 unhesitatingly, certain definite ages to the series (b) and (a), and 

 that, too, mainly on the strength of the occurrence in the latter of 

 certain groups of Graptolites. The Skiddaw Slates may be con- 

 sidered to be of Lower Llandeilo age, as long ago surmised by Mr. 

 Salter and believed by Professor Nicholson ; but the} r may represent. 

 several of the subdivisions of the Welsh Lower Silurian, and I shall 

 presently bring forward some physical evidence to show the possi- 

 bility of this latter surmise. At any rate, this much is evident, that 

 the mountain district of Cumbria is made up of rocks of great age, 

 and we may consider all the material that now enters into the 

 formation of our Lake District Mountains to have been formed ere 

 the lowest beds of the great Carboniferous System were laid down, 

 and at the present day the beds of Carboniferous Basement Con- 

 glomerate and overlying limestones, sandstones, and shales form a 

 rough circular framework to the older and mountain-forming rocks 

 of Silurian (or Silurian and Cambrian) age, as shown in the Sketch- 

 Map (Plate II.). We will now consider in succession the physical 

 conditions which probably prevailed during each succeeding period 

 of the history of Cumbria, giving first the leading facts in short 

 abstract, and then dwelling on the conditions which those facts 

 indicate. 



Part I. — Physical Conditions of each Period. 

 A. — SMddaw Slate Period. 



As the name indicates, many of the rocks formed during this period 

 have now a slaty character. The total thickness of the whole series 

 we do not know, for no defined base is met with ; but there must, I 

 think, be at least a thickness of 10,000 or 12,000 feet of beds 

 included under the head of Skiddaw Slates. We will return to the 

 consideration of possible subdivisions of this formation, later on. 



Cleavage is undoubtedly a characteristic feature among the rocks 

 of this series, and is best exhibited among the fine black slates of the 

 west and south side of Skiddaw. In such slates it is sometimes 

 exceedingly difficult to determine the original bedding, and where, 

 as in many cases, a system of close jointage, and sometimes a species 

 of secondary cleavage, occur, the task is made still more difficult, or 

 quite impossible. These slates, representing old marine muds, are 

 those beds which most frequently contain fossils — as Graptolites, a 

 few Trilobites, Phyllopod Crustacea, etc. Sometimes interstratified 

 with the black slates, and sometimes forming thick masses by them- 

 selves, occur bands and beds of sandy mudstone, sandstone, and 

 coarse grit. The flags are frequently ripple-marked, and show worm 

 tracks. The grit occasionally passes into a true conglomerate, with 



1 In conformity with Survey nomenclature used in previous work, I here call the 

 series above the Coniston Limestone, Upper Silurian, and when speaking generally 

 of the physical relations of one group to another, I use the term to include all under 

 the head of (c). 



