160 TF. M. Hutchings — Ash-slates of the Lnke-Distrid. 



Comparing A. and B., the most striking fact is that though the 

 removal of the chlorite and calcite has tripled the potash-percentage 

 in the residue, the soda has not only not kept pace with it, but lias 

 actually diminished, so that much the greater part of it has been 

 removed by the digestion with moderately strong acid. 



As regards the form in which the soda is contained in these 

 samples, it is not possible to make any definite statement, as the 

 microscope does not assist us. There is hardlj' a trace of clastic 

 felspar to be identified ; how much may be ])resent as minute dust 

 still, or as secondary material in the fine mosaic, cannot be ascer- 

 tained. 



The solubility of so large a part of the soda may be explained 

 in two ways. Zeolitic minerals exist in these rocks, and though 

 nothing can be made out microscopically in this instance, there may 

 be a considerable amount of soda-zeolites finely disseminated. 



There is another explanation which may not improbably be com- 

 bined with the above, viz. that this particular band of slate was 

 formed from an ash much more basic than in the case of the Mose- 

 dale and Kentmere bands. It may be noted that the most basic 

 rock hitherto observed in the Borrowdale series occurs near Gras- 

 mere (Geol. Mag. Dec. 1891, p. 538), and some of the coarser ashes 

 in the neighbourhood also point to basic rocks. 'J'he fine slate now 

 under consideration is traversed by bands of coarser material. One 

 of these, within an inch from where the material for analysis was 

 taken, though obviously originally compcx^ed largely of lapilli, is 

 now almost wholly made up of grains of chlorite and calcite, point- 

 ing to rocks more basic than the usual andesites as having been 

 largely among the components. The finest dust of such material 

 would contain moi'e labradorite, or other basic felspar, than do the 

 andesites. The removal of much calcite and iron in solution, during 

 decomposition of the augite, etc., of such dust, would cause a relative 

 enrichment as to silica and alkali (A. is richer in alkali than most 

 ashes and other rocks in the district). Finally, alteration of the 

 fine ash may be here less complete than in the cases previously 

 dealt with, and there may still be some labradorite, etc., pi'esent, 

 finely divided, and attacked during digestion in acid. 



Of the soda which remains in B. some part may be in the mica, 

 and a part — probably the larger part — as felspar. Some of this 

 felspar may be original dust of more acid felspars, but it is more 

 likely that it is in the lorm of " regenerated " felspar in the mosaic 

 wilh the quartz and mica. Examination of the coarser ashes and 

 tuffs, as well as andesites. of this district, shows the regeneration of 

 felspar (albite, andesine?) to be most abundant and widesjiread 

 (see further on), and though the microscope is not able to demon- 

 strate it in the very fine-grained mosaic of this " base " of the slates, 

 it is quite reasonable to suppose that such regeneration has in some 

 cases taken place there also, under the same conditions of chemical 

 change and intense dynamic action. 



At any rate, whatever be the correct explanation of the chemical 

 facts as to this particular slate, we see that, taking these rocks as 



