-*324 MESSRS. A. HARKER AND J. E. MARR ON 



as we approach the granite, and, with few exceptions, the rocks in 

 the vicinity of the contact have been completely reconstituted. 

 Our results, however, lead to the conclusion that any division of 

 the aureole into distinct rings or zones would be arbitrary and arti- 

 ficial, and certainly could not be made to apply alike to the various 

 kinds of rocks metamorphosed. In the andesite.s, for example, the 

 transition from the least altered to tlie most altered types is so 

 gradual that no lines of division can be drawn either in the field or 

 by minute examination. In the rhyolitic ashes our descriptions 

 show two different ty^pes, but the distinction of these two would 

 probabl}' resolve itself into one of degree rather than of kind, if it 

 were possible to examine the rocks between 300 and 600 yards 

 from the granite, between which limits we have found no exposures. 

 As to the calcareous beds, these have been described in other 

 districts as showing a very complete alteration to points even beyond 

 the limit of the aureole in the associated slates, though with no grada- 

 tions in metamorphism within those limits. But, although we find 

 in our calcareous rocks a high degree of metamorphism extending to 

 a considerable distance from the actual contact, this seems, so fai- 

 as we can judge from the rocks exposed, to die away gradually to 

 the boundary of the aureole. The flags in the Shap district are 

 not well enough exposed to warrant any sweeping conclusions, but 

 it would be difficult to draw any divisional line in those seen within 

 the metamorphic region. Zones of metamorphism may perhaps be 

 usefully laid down in certain cases, as, for instance, when a mineral 

 like chiastolite is developed in the outer part of the aureole and 

 disappears in the inner; but such divisions do not appear practicable 

 in the Shap Pell district. 



It is noticeable that the chemical effects of the metamorphism 

 were first produced in those constituents of the rock which owed 

 their origin to weathering, decomposition, &c., such as delessite, 

 calcite, and carbonaceous matter. In other words, the substances 

 which had been formed under normal atmospheric conditions were 

 the least stable when subjected to the high temperature which 

 accompanied the intrusion of the granite. The minerals of direct 

 igneous origin in the volcanic rocks were less susceptible to thermal 

 metamorphism, and the original quartz-sand in the flags proved 

 especially refractory. 



The several minerals detected in the various metamorphosed rocks 

 as products of the metamorphism are summarized in the table 

 given below. The absence or rarity of some characteristic " con- 

 tact-minerals " of other districts is rather striking. Some of these 

 are products which probably require special " mineralizing agents '' 

 to co-operate in their manufacture ; such as fluorite, tourmaline, 

 lithionite, and axinite ; but the almost complete absence of anda- 

 lusite, staurolite, and garnets (other than lime-garnets) is more 

 remarkable. 



In the table the occurrence of the minerals in the different rocks 

 studied is marked by an asterisk (*). Parentheses ( ) indicate 

 rarity or occurrence only under special conditions, e.g. in the vicinity 



