PRECAREONIFEROUS ROCKS OP CHARNWOOD FOREST. 211 



tuff can hardly have been otherwise produced, yet this is a more 

 fragile mineral. Slides of the agglomerates from the Queen's Drive, 

 Arthur's Seat, show quartz grains extremely like some of those in 

 the Charnwood rocks. These can hardly be other than fragmenta], 

 for the rock is not highly altered. The whole structure indeed 

 recalls that of some of the Charnwood rocks. A slide of basaltic 

 agglomerate from a rock at Elie, Fife, even shows several small 

 quartz grains almost certainly clastic. 



It may perhaps be felt that the absence of lava-flows is a diffi- 

 culty in claiming a pyroclastic origin for so many of these beds. It 

 is doubtless a difficulty, but not without some parallel. Mr. Clifton 

 Ward's map of the Borrowdale region (and whoever has had the 

 pleasure of seeing him at work knows that he is not likely to have 

 overlooked any thing important) shows that there the proportion of 

 the lava-streams to the ash-beds is very small, and in the Charnwood 

 area exposures are less extensive, and continuous sections far less 

 frequent than in the Lake-district. Again, in parts of the Eifel also 

 there is but little lava, and in the Pklegrsean fields extremely little. 

 The rarity of conglomerate, grits, and rounded detrital materials 

 seems to indicate the absence of either rivers or tidal currents. 

 Such a district, then, as the Phlegraean fields, consisting of many low 

 craters, from which steam and ashes were discharged, standing near 

 lakes or lagoons, would seem to supply the condition required for 

 the formation of these Charnwood rocks. The lowness of the hills 

 and porosity of their materials would be unfavourable to rivers ; 

 the ash would settle down in quiet waters, little rolled, or be spread 

 out upon the plain. The land, owing to the frequent showers of 

 ash, might be unfavourable to vegetation, and the volcanic disturb- 

 ances might render the waters unprolific. 



The Igneous Rocks of Charnwood Forest. 



(1) Preliminary. — The true igneous rocks of the Charnwood-Forest 

 area may, for convenience of description, be arranged under four 

 heads. These are (a) the Southern Syenites, (6) the Northern Syen- 

 ites, (c) the Granites of the Quorndon district, (d) the Later In- 

 trusive Hocks. As is well known, some authors have expressed 

 doubts as to whether the first three of these might not be highly 

 metamorphic sedimentary rocks. Now T in speaking of igneous and 

 metamorphic rocks we must, of course, understand distinctly in what 

 sense we use the terms. It is doubtless conceivable that a sedi- 

 mentary rock might be melted down in situ by hydrothermal action, 

 and recrystallizcd so as to be undistinguishable from a molten mass 

 which has been forced upwards from the interior of the earth. 

 Several instances of this have indeed been adduced ; but the evidence 

 on examination often proves defective, as one of the present authors 

 has more than once ascertained. Further, if a rock were thus 

 melted in situ, it might by earth movements be squeezed from its 

 original position into a new one. In this case its demeanour would 

 be identical with that of a true igneous rock ; but then, as all trace 



