W. M. Hutchings — Coniston Flags at SJiap. 461 



the comparatively clear " spots " which are so prominent a result of 

 the alteration of these rocks. In this I have not been successful. 

 All the spots, however, are not of the same nature. In some cases 

 they appear to consist almost wholly of white mica. In others, after 

 much observation and comparison with other contact-sj)ecimens, I 

 am of opinion that, as suggested by Harker and Marr, andalusite is 

 the mineral being formed. But that mineral, in definite recognizable 

 form, does not occur in any of my sections. In other slides, again, 

 the material of the spots is quite different from either of the pre- 

 ceding and quite beyond any attempt at identifi.cation, 



Messrs. Harker and Marr are of opinion that probably a good deal 

 of felspar is formed in these altered flags, together with the mosaic 

 of regenerated quartz. There are few questions of greater interest 

 than that of the formation of new felspar in sedimentary rocks, 

 whether by contact or by regional metamorphism, and any instance 

 brought forward is important. Such instances are not very numerous, 

 and some of them do not appear to be by any means fully accepted. 

 In the case of these rocks in Wasdale Beck I have made every effort 

 to obtain proof of the occurrence of felspai', but without any success. 

 All the grains of the mosaic are perfectly limpid. Many suggest 

 felspar by their outlines, as stated by Harker and Marr, and there is 

 decidedly an impression produced that the mineral is there. But of 

 scores of tests in convergent light, made on promising-looking 

 grains, not a single one has given proof of a biaxial mineral, which 

 would in this case be sufficient confirmation. The sections for 

 studying this class of rock are necessarily very thin ; but with 

 equally thin slices of some of the neighbouring altered volcanic 

 rocks with quartz-felspar mosaic, it is quite easy to pick out and 

 identify the felspar grains. Although it is by no means unlikely 

 that felspar is present, I prefer to consider it as not proved, so far 

 as any of my own specimens are concerned. 



Although on a minuter scale, great interest attaches to the changes 

 which are undergone, during the alteration of rocks in this class, 

 by the minerals consisting wholly or largely of titanic acid ; and 

 these flags of Wasdale Beck are specially suited for observing these 

 changes, as we may here see several of them together which have been 

 noticed elsewhere singly by different observers at difi"erent places. 



At the falls near the hotel, where alteration is already well 

 advanced as regards formation of brown mica and is distinctly com- 

 mencing as regards regeneration of quartz, we still see the original 

 " clay-slate fieedles " in considerable numbers. They are of very 

 small size. The only change seems to be that they are not as equally 

 diffused as in the original rocks, having apparently commenced to 

 disappear at some parts of each slide examined. A few yards higher 

 up, with much increased development of brown mica and regenerated 

 quartz, these minute rutiles have disappeared ; and in due course, 

 as the new limpid mosaic is developed, we note the appearance of 

 rounded and ovoid grains of rutile and of crystals of that mineral, 

 which are much larger and relatively thicker and blunter than the 

 original needles. These things, together with other indeterminable 



