W. 31. HutcMngs— Rocks of Great Whin Sill 79 



In tlie nodules considerable fields of clear, almost colourless, quite 

 isotropic material are seen, in which bundles and sheaves and 

 psoudo-spherulites of felspar, with some quartz, have been formed. 

 Anthophyllite and andalusite are also seen in some of them. 



Here, again, we have preserved for us one of those interesting 

 cases of interrupted development. All the finer-grained material 

 of the shale, — the impure micaceous mineral and the minuter quartz, 

 — has been taken up into solution, or aqueous fusion ; and out of the 

 substance so formed a mosaic of quartz with some felspar, together 

 with muscovite, has been in process of crystallization. But this 

 process was arrested before it was complete, and so we are again 

 able to see the unfinished stages, to observe the residual indefinite, 

 isotropic, intermediate matter, and to note also the larger quartz- 

 grains which were being attacked and dissolved, and would have 

 all disappeared if the solution stage of the contact-action had been 

 able to continue somewhat longer. 



Sections from other parts of this bed show us mainly a fine- 

 grained aggregate of newly-formed quartz and felspar, passing down 

 into a quite cryptocrystalline felsitic-looking mixture (adinole), but 

 opening up, on the other hand, here and there into numerous clear 

 and glassy patches, which in polarized light are seen to consist of 

 groups of well-twinned, plagioclase felspar, which can often be 

 identified as albite, whilst the extinctions also point to the presence 

 of a species allied to oligoclase. 



From tlie neighbourhood of Rowntree Beck, again, come specimens 

 of shale altered to adinoles, and showing nodules up to two inches 

 across, with anthophyllite. 



We come now to the calcareous shales, and find that among 

 these we have some of the most intensely altered rocks of all. 

 Sometimes they occur as narrow bands in connection with purer 

 limestones, sometimes as patches and lenticular masses in such 

 limestones, and sometimes as thicker independent layers. 



The most striking occurrence is at Falcon Clints. The specimens 

 show a compact hornfels-like brown rock, with a jaspery sort of 

 appearance and fracture. It contains many garnets of sufficient 

 size to be easily seen with the naked eye. Thin sections show that 

 these garnets are the most prominent mineral contained. They 

 very much resemble those in the altered impure limestones round 

 the Shap granite, and like them are polysynthetic and show a good 

 deal of birefraction. They are, however, here not so often well- 

 defined crystals, but more irregular grains and patches. They are 

 often very much cracked, the cracks being infilled with chlorite 

 and other substances. They occur irregularly, some parts of the 

 rock being free from them and others containing swarms of small 

 grains and crystals. 



In some specimens idocrase occurs with the garnet, some of it as 

 good large, well-defined crystals on which characteristic angles can 

 be determined. It is nearly all quite fresh and good, and in every 

 way of normal chai-acter. 



Both garnet and idocrase crystals may be seen containing large 

 numbers of small crystals of spinel, the garnet much more so than 



