(art 2] GEOLOGY OP THE MELDON VALLEYS. 8 



Meldon aplite contains blue apatite, but practically no tour- 

 maline. 



Admittedly, this almost pure aggregate of lithia-mica as the 



ultimate and extreme form of contact-alteration of the shales is 

 surprising. But the evidence is absolute, and in sonic places the 

 thin end of a large wedge-shaped inclusion will take this form, while 

 the porcellanite type occurs where the inclusion is more massive. 



It is interesting to note that the tourmalinization of the calcareous 

 shales by the Meldon aplite is negligible, being confined to slight 

 action on the smallest inclusions; fluorite docs not occur in the 

 shales, hut in Q. Ill, the most massive fluorite vet found occupies 

 cracks in an inclusion of 'dark igneous' rock; axinite is confined to 

 near the margin of the dyke; datolite does not seem to he present 

 in any slide as yet prepared. In other words, those minerals which 

 might arise by fluoric and horic emanations from the dyke are 

 practically absent in the shales, the secondary minerals of which, 

 although some may conceivably contain fluorine or boron, or both, 

 are yet such as, in the absence of these problematic constituents, 

 may have been derived from the recombination of materials present 

 in the unaltered shales. Perhaps the addition of a little soda may 

 have been necessary, but even this is not certain. And yet the 

 dyke itself is rich in fluorite, topaz, tourmaline, and in fluor-apatite. 



The larger inclusions of shale will be more fully dealt with 

 ■under the heading ' Meldon Aplite ' i § VI, p. 98). 



The Meldon Limestone. 



Unfortunately, specimens of this rock are now only obtainable 

 from the quarry- waste. It is dark blue-grey, almost black : on 

 solution in acid the pigment forms part of the residue, and. since 

 it disappears on ignition at a bright red heat, it is almost certainly 

 amorphous carbon. The acid solution yields a little alumina, and 

 apparently no magnesia. There is always some residue besides the 

 pigment, but quartz-grains are not present. 



Certain specimens show small excrescences on their weathered 

 feces, and dilute acid emphasizes these excrescences. Such speci- 

 mens if treated with hot acid leave spongy black fragments, porous 

 from the solution of the carbonate. Uncovered sections show 

 patches of higher polish, but even in the thinnest section the calcite 

 masks the presence of any other mineral : treated with dilute acid, 

 however, patches are left in which this mineral, although per- 

 forated and honeycombed, shows simultaneous extinction over 

 areas about equal to the field of a ( l-inch objective. From such 

 rock the portion soluble in acid contains a little magnesia, while 

 the insoluble portion yields silica, iron-oxide, magnesia, lime, 

 and manganese this last substance being present throughout the 

 calcareous series. 



l'adiolarian chert occurs both above and below the horizon 

 of the limestone. It is in contact with a narrow vein of the "dark 



