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The other problem alluded to as engaging Harkness's attention 

 about this time, was intimately connected with the subject of the 

 controversy that had then long been, and indeed, still is, raging 

 between the partisans of Murchison, and such students of Geology 

 as are of opinion that Sedgwick was entitled to much more credit for 

 the results of his long labours on the older Palaeozoic rocks than the 

 equally able but more energetic and methodical author of the Silurian 

 System had seemed to many willing to admit. It would be out of 

 place here to give even an outline of the evidence adduced in 

 support of the views of either party ; but it may suffice to explain 

 the nature of the investigations Harkness was now taking a part 

 in to state that what Murchison originally meant by Silurian was 

 all the rocks from the base of the Hereford "Old Red" down to 

 the lowest horizon where the occurrence of fossils had at that time 

 been clearly proved. This line was then generally regarded as 

 coincident with the great stratigraphical break known to exist 

 between what is now called the Upper Silurian and the Lower. 

 All the stratified rocks below this stratigraphical break were called 

 by Sedgwick Cambrian, and they were at first supposed to be 

 entirely devoid of traces of hfe. Bye and bye fossils began to be 

 found at lower and lower horizons ; and as these facts were made 

 known, the base of the Silurian System was taken lower and lower, 

 so as to coincide with the lowest known life-zone. At the time 

 I am about to refer to, the Lingula Flags were usually regarded as 

 the base of the Lower Silurian by Murchison, But Dr. Hicks had 

 been hard at work at the older rocks, and had succeeded in 

 disclosing evidence of a richly fossiliferous zone lower even than 

 the Lingula Flags. A good idea of the nature of these fossils may 

 be gathered from an inspection of the Menevian fossils, as these 

 are called, that Harkness collected with Hicks, and that are now 

 in the Museum at Carlisle. It was the discovery of this older life- 

 zone that necessitated a still further modification of the base line 

 of the Silurian System, and a consequent modification of the views 

 that Sir Roderick had himself already published. There is inde- 

 pendent evidence, beside what appears here, that Harkness was 

 entering into the discussion of this subject with considerable ardour, 



