ANNIVEKSAllY ADDKESS OF TUE J»KES1DENT. 1 43 



Some of the pieces of slate arc six or eight inches long and arc now 

 placed parallel to tlie cleavage of the rock. Among the slate 

 debris, however, felspar crystals and felsitic fragments may be 

 observed. Bands of coarser and finer green tuif show very clearly 

 the bedding in spite of the marked cleavage. 



But throughout the whole volcanic group the material of the tuff 

 is chiefly of thoroughly volcanic origin, and its distribution appears 

 to agree on the whole with that of the bedded lavas. In the older 

 portions of the group it is probably mainly derived from andesitic 

 rocks, though perhaps with an occasional intermingling of felsitic 

 detritus, while in the higher parts many of the tuffs are markedly 

 felsitic. Some of the ejected ash must have been an exceedingly 

 fine dust. Compacted layers of such material form bands of green 

 slates, which may occasionall}^ be seen to consist of alternations of 

 coarser and finer detritus, now and then false-bedded. Such tuffs 

 bring vividly before the mind the intermittent explosions, varying 

 a little in intensity, by which so much of the fabric of the Lake 

 mountains was built up. Breccias of varying coarseness are like- 

 wise abundant, composed of fragments of andesite and older tuffs 

 in the central and lower parts of the volcanic group, and mainly of 

 felsitic detritus in the upper parts. Some of these rocks, wherein 

 the blocks measure several yards across, are probably not far from 

 the eruptive vents, as at Sourmilk Gill and below Honister Pass. 

 Generally the stones are angular, but occasionally more or less 

 rounded. Stratification can generally be detected among these 

 fragmental rocks, but it is apt to be concealed or effaced by the 

 cleavage, while it is further obscured by that widespread indura- 

 tion on which Mr. Ward has laid so much stress. 



Little has yet been done in identifying any of the vents from 

 which the vast mass of the volcanic material of the Lake District 

 was ejected. Mr. Ward believed that the diabase boss forming the 

 Castle Head of Keswick marks the site of " one of the main volcanic 

 centres of this particular district " *, whence the great lava-sheets 

 to the southward flowed out. There are obviously two groups of 

 bosses on the northern side of the district, and both of these, in my 

 opinion, may mark the position of vents. Some of them are occu- 

 pied by more basic, others by more acid rocks. It is not necessary 

 to suppose that the andesitic lavas ascended only from the former 

 and the felsites from the latter. While the felsites on the whole 

 are younger than the more basic lavas, they may have been erupted 



^ Op. cit. p. 70. 



