66 W. M. Hutchings — Clays, Slates, and Contact-MetamorpMsm. 



abundant in some parts of the Shap contact near to the granite 

 outcrop. Some slides from these parts are very closely paralleled 

 by examples from the Elbe Valley contacts described by E. Beck 

 {op. cit.), who says of some of them, " Cordierite represents the spots 

 of the Knotenglimmerschiefer, which do not otherwise form any 

 definite minerah" The cordierite of the Shap rocks is not in any 

 way distinguishable from that of some of the rocks from the district 

 described by Beck, sections of which I have examined, and also 

 closely resembles the occurrences in rocks from the Lausitz district 

 of Saxony. This, then, is another case in point where a definite 

 mineral is formed in a rock wherein the real " spots " have not yet 

 wholly died out, though less abundant than in the outer zones. 

 There is nothing really to lend weight to the idea that any of these 

 spots consist of andalusite, and this mineral is not detected in any 

 of the altered sedimentary rocks at Shap. 



Other spots, as previously stated, consist almost wholly of white 

 mica, newly formed and full of quartz-grains and other things in 

 the usual manner of this newly-formed contact-mica. 



With these, and still more as we recede from the granite outcrop, 

 are the true " spots," more or less closely resembling those above 

 described, containing the substance in question in all its stages from 

 amorphous, through minutely cryptocrystalline up to a definite 

 micaceous development. And the same substance occurs in some 

 slides outside the spots, or where these are quite absent, lying in 

 among the mosaic minerals or surrounding them in the usual 

 characteristic manner. 



It remains to consider what may possibly be the nature of the 

 substance seen so abundantly in the contact-slates from widely 

 separated localities, and what are likely to be the processes to which 

 it, and some of the other phenomena observed, owe their origin. 



The first thing to remark is that the substance in question, what- 

 ever may be its exact nature, is certainly quite a new formation. It 

 does not correspond to anything that can ever be observed in 

 normal slates or shales, and we see that when it first makes its 

 appearance in the slates, at the outer parts of contact-zones, it is 

 mainly limited to "spots" and is in some way correlated to the 

 " aggregations of dark grains " ; also that these dark grains are very 

 frequently to a large extent small plates of ilmenite, or crystals of 

 anatase, or re-formed crystals of rutile, all of which either did not 

 exist in the normal slate, or existed in a different form and not 

 aggregated. If we consider how these aggregations of recrystal- 

 lized minerals were caused, we cannot very well conceive of any 

 process by which they migrated, recrystallized, and aggregated 

 together as siich. Thus, taking the simplest case, that of rutiles, in 

 which a mineral has simply increased in size and aggregated, and 

 not a case in which its material has reappeared in a new form, as 

 rutile changed to anatase, or combined with iron-oxide as ilmenite, 

 — we cannot assume that for each one of the larger and more perfect 

 crystals seen, several of the minute " clay-slate needles " have 

 travelled in the rock and simply combined to make one larger 



