W. M. Hutchings — An Interesting Contact- Roch. 127 



on snch alterations in the Harz and elsewhere. They are also seen 

 at other parts of the Whin Sill contacts, besides the locality with 

 which we are now dealing. They are known as adinoles, and will 

 be so spoken of in what follows. A large part of the typical adinoles 

 shows the mixtui'e of quartz and felspar in a quite unresolvable, 

 cryptocrystalline condition, and its true nature, apart from chemical 

 evidence, can only be ascertained through the circumstance that 

 nearly all occurrences of it open up here and there, in perfect 

 continuity, into patches of so much coarser grain that the com- 

 ponents can be clearly made out. 



It is usual to designate as adinole more specially the contact-rock 

 close to the intruded igneous mass, and to associate with the name 

 also an increased percentage of silica, which it can be shown in 

 many cases to possess. But there are many reasons, upon which 

 I need not enter here, why these restrictions should not be placed 

 upon the name, and in favour of the rationality, in adopting the 

 term, of applying it to all the alteration-products of shales, slates, 

 etc., by basic intrusions, in which a fine-grained mixture of quartz 

 and plagioclase has resulted. 



As regards the nodules, they vary mineralogically in every degree 

 of qiianlitntwe composition, but seem to be all due to the difi'erent 

 degrees of the same processes indicated above. Many of them 

 show nothing beyond an aggregation of pigment, and a quite narrow 

 ring of material differing from the rock outside and inside their 

 areas. These occur in parts of the rock which are not so much, 

 affected by re-solution of materials. The quartz-grains are very 

 little attacked in these cases, and are the same inside as outside 

 the ring. Such nodules are really to be described as mere shells 

 of a special alteration-product, enclosing areas of the less altered 

 or differently affected material among which they have been formed. 

 In other nodules, again, the shell widens and can be better studied, 

 and it is seen that instead of fields of isotropic matter with sheaves 

 and spherulites of felspar and quartz, we often have the adinole- 

 material varying from cryptocrystalline to microcrystalline. In 

 such bands the clastic quartz is in all stages of disappearance. 

 Sometimes it is quite gone, but more usually corroded grains may 

 still be seen, the final stage being that only small blebs and speckles 

 of it remain to show where the larger grains once were. Where 

 the shell is of any considerable width it is very often distinctly 

 banded in concentric layers of more or less varying colour, and 

 it frequently varies also in the degree of crystalline development 

 in these layers. There are also frequently concentric cracks in 

 these shells, which appear to indicate some strain during final 

 cooling of the rock, or more probably during the final consolidation 

 and crystallization of the material forming the shells. 



These shells of more considerable width still surround and enclose, 

 in most cases, a kernel of the altered rock, similar to what exists 

 outside, but there are also cases in which the entire nodule consists 

 of this adinole material, and we have then approximately spherical 

 bodies of more or less banded substance, yellow to brownish in 



