i3i 



THE SUCCESSION OF THE SILURIAN ROCKS 



OF INGLETON AND THE 

 INCLUDED TRAP DYKES OF MOST INTEREST. 



ROBERT R. BALDERSTON. 



For a long period it has been supposed that only two trap-dykes of 

 any great interest and thickness are to be observed in the Silurian 

 rocks of Ingleton, although allusion has been made by various 

 authorities to a ' large series of trap-rocks ' as being found, of vast 

 vast thickness, amongst the Green Slates of this district, but whether 

 these were regarded as dykes, intrusions, lava-flows or volcanic 

 ejectamenta redeposited along with beds that were plainly composed 

 of sedimentary ash, has been a point very vaguely demonstrated. 



As the result of a considerable amount of labour recently spent 

 in the examination of the beds in question, I have drawn up a list 

 of those rocks which appear to me more or less clearly entitled to 

 be regarded unequivocally as igneous intrusions or eruptive, whilst 

 associating those other rocks, which have until recently been classified 

 as ' a great series of trap-rocks,' with the sedimentary division. 

 This has been done owing partly to a study of the questionable series 

 in relation to their mineralogical appearance and constitution, and in 

 part to their physical relation to the slates and ash-beds with which 

 they are associated. To this group of rocks, which is harder and 

 often more massive than the typical slate, I shall refer under the 

 term ' Galliard,' a name of local application, and one not likely to 

 give a too definite and perhaps erroneous description as would the 

 words 'grit,' or 'trap.' The galliards have been described — and 

 more particularly group 6 of my appended series — as 'massive 

 felspathic trap of great thickness, and intersected by numerous bands 

 of quartz,' they have been also further correlated with the interbedded 

 felstones of the Lake District; a close examination, however, dis- 

 closes that these rocks are not so massive as has been supposed: — 

 i. That in many places they are distinctly notable for slaty 

 cleavage, but have a crystalline character. 



2. That in a still greater number there is only a partially- 



obliterated slaty cleavage, the crystalline or coarser element 

 having only partly invaded the cleavage planes. 



3. That where the more massive character is conspicuous, the 



bedding planes very frequently divide the rock regularly, 

 and in correspondence with the coincident cleavage, into 

 thin or thick slabs, or occasionally, in rarer instances, large 

 well-defined blocks. 



May 1889. 



