318 ME. J. B. HILL ON THE [Aug. IQOI, 



nevertheless met with in a highly decomposed condition, in which 

 the hornblende has complete!}^ broken down ; but tiny felspars often 

 remain. When these latter are absent the igneous character of 

 the rock is obliterated. In this condition the rock becomes very 

 calcareous, arising from the breaking down of the lime-bearing horn- 

 blendes and felspars, and partly, doubtless, from the decomposition of 

 the big limestone-masses with which these rocks are associated. 

 That these green calcareous schists are the products of the alteration 

 of the epidiorite there is abundant evidence to show. Cores of epidi- 

 orite of various types may be followed from their normal fresh 

 condition, passing gradually outward into these nondescript green 

 calcareous schists. When rocks of this type are interfolded with 

 sediments, it is often a matter of extreme difficulty to separate them 

 from very similar calcareous beds of sedimentary origin. In some 

 cases boulders derived from this material have been looked upon as 

 sedimentary, which has led to the crush-conglomerate being mistaken 

 for the Boulder-bed. 



Epidote is commonly distributed throughout the epidiorite-mass 

 as grains in the rock, or in a more massive condition in cores, veins, 

 and strings, intermixed with quartz, and forming epidosite. 

 Cores of epidosite, from a few inches to a foot or more in their 

 longest diameter, pervade all the varieties of the rock, and in the 

 calcareous chlorite -schists are often the sole remaining link which 

 connects them with the unaltered epidiorite. 



The intimate nature of the interfolding will be a])parent from 

 the following illustration. The country bordering Inverliver on 

 Loch Awe perhaps comprises the least altered rocks of the district, 

 both igneous and sedimentary. Here grits and slates may frequently 

 be seen quite unaltered, having suifered very little from the effects 

 of crushing. The big igneous sill presents a similar condition, the 

 porphyritic felspars of idioraorphic character have generally suffered 

 little or no alteration, and the rock has none of the characteristics 

 of an epidiorite, but preserves structures which are truly igneous, 

 and appears in the field as bands of more or less altered andesites 

 orandesitic dolerites divided by bands which are more sheared. 

 In the section, for instance, at Eilean Liver, bands rich in 

 porphyritic crystals of idiomorphic felspar alternate with layers of 

 chlorite-schist in which the porphyritic felspars are absent. With 

 these compact bands are alternations of the same material but very 

 vesicular, some of the vesicles being filled with quartz and others 

 with calcite, while some cavities are empty, and occasionally we 

 see thin strips of limestone. The whole has a very bedded appear- 

 ance, with the respective bands of alternating material dipping at 

 a high angle and averaging about a foot in thickness. 



Numerous sections along the northern coast of Loch Awe may 

 be observed, presenting similar characters. IS'ear Arichamish, 

 however, about 1 mile east of Inverliver, igneous rocks of this 

 character are seen divided by a band of grit, and instead of a 

 normal junction between the two rocks the line of demarcation is 

 represented by a complex of minute folding, strips of fine grit 



