134 BALDERSTON : THE SILURIAN ROCKS OF INGLETON. 



individualisation of constituents. Further than this I will not go, 

 except to suggest that these purple and iron-stained slates and gneiss, 

 which form the natural base of the Green Slates of the Lower 

 Llandeilo period, belong to the Arenig group. An older date we 

 cannot at present assign to the series without disproving the existence 

 of the fauna alleged to be found in its upper division, though there 

 are serious grounds for doubt. 



The thickness of the Lower Silurians of this district is practically 

 identical with the width of outcrop, as the dark, calcareous, and 

 green slates are bedded almost vertically, their cleavage, which is 

 commonly and correctly regarded as almost, or for the most part, 

 coincident with the bedding, being frequently actually vertical, and 

 always at such a high average inclination that the deduction from the 

 measurement of the width of outcrop to obtain the actual thickness 

 of the beds is so small as, for all practical purposes, to be 

 absolutely nil. 



The stratification of the Lower Silurians in no way directly 

 corresponds with that of the Upper division, a very marked uncon- 

 formability existing between the two series, and if at any point there 

 should happen to be an appearance of conformability, this is merely 

 due to the rolling nature of the bedding of the upper group, a 

 feature not observed in the underlying series, in which the folding of 

 the beds was complete previous to the Upper Silurian epoch. This 

 point appears to have escaped the attention of the field geologist, and 

 the dilemma to which its non-recognition leads has obviously been 

 avoided or explained by the suggestion of a fault at every place 

 where the relations of the two series are exposed, and appear 

 to be otherwise irreconcilable. Such a conclusion, if true, forms a 

 very easy solution of the question, and one not taxing the brain with 

 much thought as to how the various formations were originally 

 related. 



UNCONFORMABILITV. 



Middle Llandeilos. Upper Silurians. 



Dip 72 to S.YV ! Nearly level ) Dowgill and 



Strike of Cleavage to N.W....! To W. by N ) Brackenbottom. 



Dip 70 to S.S.W. 

 „ 84° to S.W. 

 ,, 70 to S.W. approximate 



All full of trap-dykes 



6o°toN.E Wharfe. 



Nearly level ... ... Ingleton. 



Nearly level at point of ) Hd m . 

 overlap ... ...J 



Dykes absent. 



It is plain, however, that an indented sea-coast with somewhat 

 abrupt estuaries, such as the fjords of Norway, but on a smaller 

 scale, existed in the district along the flanks of the Upper Silurian 



Naturalist,. 



