1XXX PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May I906, 



As regards their age, the evidence is in favour of the greater 

 number having been produced in Devonian times. The more 

 easy detection of those in the centre of the district might be 

 regarded as a proof that they were actually more abundant there, 

 and that they were produced, during the later movements which 

 caused the dome, as radial cracks from the centre ; but they do not 

 appear to have any radial arrangement. On the contrary, the more 

 usual trends are in two directions roughly at right angles, namely, 

 about north-north-west to south-south-east and east-north-east to 

 west-south-west, corresponding with the general dip and strike of 

 the Lower Palaeozoic rocks produced in Devonian times ; while the 

 three dominant belts, the trend of which has been noticed in detail, 

 radiate from a tract where the strike of the rock changes rather 

 abruptly from east-north-east and west-south-west to north-east 

 and south-west. 



Detailed examination of some of the belts shows that the 

 fracture of the rock was often accompanied by other changes, 

 similar to those which can be proved to have taken place in 

 Devonian times. A well-marked belt runs up Raise Gill to the 

 east of Watendlath Tarn. The rocks along this have been, in some 

 cases, crushed into a mylonitic mass, the porphyritic felspars being 

 flattened into flaky patches ; cleavage-planes have been formed, 

 and these in places chevron-folded ; and a development of sericitic 

 mica has been set up along the planes. 



The evidence, then, is in favour of the bulk of these shatter-belts 

 being along tear-faults. Most of the mineral lodes inserted on the 

 maps of the Geological Survey have been formed along these belts, 

 though occasionally a lode is found along the more horizontal 

 lag-faults. But an examination of the lodes on the map gives a 

 good idea of the general distribution of the shatter-belts, though, 

 of course, a large proportion of the belts do not contain sufficient 

 ore to allow of their representation as lodes. 



Owing to the lag- and tear-faults the district is cut up into 

 blocks of rock of a more or less rhomboidal nature. These rhom- 

 boidal blocks are of all sizes, from masses several miles long to the 

 fragments of an incipient fault-breccia. In the case of the breccias 

 rounding has often gone on to such an extent as to produce fault- 

 conglomerates ; and the same seems to have been produced on a 

 somewhat larger scale, leaving ' eyes ' of hard rock surrounded by 

 broken material. Hence, it is only where the rocks have been 

 slightly affected by movement (as in the Eycott Group on the north 



