718 ME. J. E. MARE AND DE. H. A. InTLCHOLSON 



All examination of this table shows a general thickening-out of 

 the beds eastward. There are doubtless some errors in it, owing to 

 difficulties of measurement ; for instance, we feel that the thickening 

 of the Clingani-bsLTid from one to three feet in crossing the valley of 

 Long Sleddale is unlikely, and the apparent increase may be due to 

 our having included shaly mudstones in this bed at Browgill. 



Some of the variations may also be due to a greater compression of 

 beds in one locality than in another, and to portions having been 

 torn away without our detecting it, which is very possibly the case 

 in some instances where the section is not very clean-cut. But 

 with these allowances, the fact of a general thickening to the east 

 remains apparent, and is especially marked in those beds which 

 must have accumulated with considerable rapidity. The great in- 

 crease in thickness of the zones of Acidaspis erinaceus and of Mono- 

 graptus turrkulatus, the appearance of new Graptolitic seams 

 in the latter, and the incoming of the zone of Bastrites maocimus 

 in Spengill, illustrate this clearly. To what is this thickening 

 eastward due ? 



It seems to suggest the existence of land in that direction ; and 

 we are inclined to connect this with the apparent unconformity in 

 the Settle area, which possibly indicates the occurrence of land in 

 that region during the formation of the Skelgill Beds, and during a 

 portion of the period when the Browgill Beds were forming, though 

 the eZ^^ans-limestone of Austwick Beck shows that that area was 

 submerged, at any rate dui^ing the later portion of the Browgill 

 times ; but the calcareous conglomerate of Crag Hill may be actually 

 at the base of the Coniston Flags, as the ^Z^^ans-limestone has 

 not been detected here. 



We make this suggestion with diffidence at present ; after a more 

 detailed examination of other beds of this area, which we hope soon 

 to accomplish, we shall be able to express an opinion upon this 

 subject with greater confidence. 



Another point to which any one who works in a series of beds 

 like those which we have examined must have his attention called 

 is the remarkable alternation of the Graptolitic Shales with other 

 non-GraptoLitic beds. To what is this due ? to recurrent climatic 

 change, or to difference in the character of the sea-floor ? One of us 

 has discussed this question in a paper which appeared in the ' Pro- 

 ceedings of the Cambridge Philosophical Society ' (Proc. Camb. Phil. 

 Soc. vol. vi. pt. ii.), and gives reasons which induce him to consider it 

 as due to climatic change. Without entering into this question here, 

 we would call attention to another difficulty. Is the apparent absence 

 of Graptolites in the Trilobite-bearing mudstones, and of Trilobites in 

 the Graptolitic shales, due to the migration of the latter organisms 

 from the area during the formation of these shales, and to the dis- 

 appearance of Graptolites from the area during the formation of the 

 mudstones ? or did the forms linger on in the area in diminished 

 numbers during the period that was unfavourable to their existence ? 

 We cannot offer any satisfactory evidence on this point, but we 

 believe that both events went to produce the observed results. We 



