KiNAHAN — Oil Graititic and other Ingenite Rocls. 117 



associated with tuffs and agglomerates, while in composition they 

 varied from felstones (probably as in the Co. Limerick and elsewhere 

 more or less basic) to whinstones, and the different varieties of the 

 original rocks are now recorded by the variations in the metamorphic 

 rocks. The most common rock of this class in Yar-Connaught appears 

 to be an aggregate of crystals of amphibole, bluish or greenish felspar, 

 pyrite or marcasite, and a little ripidolite, mica, or such like as acces- 

 sories. It may be from finely to coarsely crystalline. Some are so 

 fine and compact that they- might be -called hornUende-aphanyte. 

 Others are an aggregate of crystals of amphibole, often apparently to 

 the nearly total exclusion of all other minerals. When very coarse 

 the crystals vary from two to four or five inches in length. These 

 rocks seem to be the typical hornblende-rock of MaccuUoch, Haughton, 

 Dana and others. A variety not uncommon has well developed crys- 

 tals of felspar, not orthoclase {dioryte) ;*' while in another variety 

 the felspar is orthoclase {syenyte), quartz also often being present, not 

 necessary as an essential but rather as an accessory ingredient. One 

 sub-variety of the syenyte is remarkable, the orthoclase being devel- 

 oped to the nearly total exclusion of the other minerals, the rock being 

 a whitish or flesh-coloured mass through which crystals of amphibole 

 are scattered ; this sub- variety {felso-syenyte) was only observed in 

 very subordinate quantities. Some hornblende-rock has orthoclase in 

 addition to the other felspars ; in a variety, Messrs. Forbes and King 

 (India) called hyperyte, hyperstene replaces the amphibole. As some 

 of these hornblende-rocks are metamorphosed diabase [pyrovene (dial- 

 lage) + felspar (not orthoclase) + ripidolite], portion of the diallage may 

 remain unaltered, or portions may be replaced by hyperstene or an 

 allied mineral, thereby forming various complicated sub-varieties of the 

 rock. 



In some varieties of hornblende-rock mica occurs as an accessory, 

 but in others as an essential {mico-hornhlende-roch). Commonly it is 

 a small black or blackish brown mica occurring more or less abundantly, 

 but besides black, white, pale sea-green, bronze, and reddish violet 

 have been observed, f Some of these rocks seem to answer the descrip- 

 tion for hersantyte of Delesse. The white and the pale sea-green mica 

 generally occurs in large flakes, while the bronze and reddish violet 



* (Gr. dioras, a clear distinction) . I would suggest that it was to rocks of this 

 class the name was originally given, as in them the minerals are always quite dis- 

 tinct. 



t Mico-hornblende-rock is called by some " micatrap." This classification 

 appears to be very vague, and evidently the group is not a petrological division. 

 Under this name they include minnette or micaceous-felstone and micaceous-elvanyte, 

 kcrsanton or micaceous-dioryte hersantyte, or micaceous-diabase, micaeeous- 

 melaphyre, micaceous-doleryte, &c., &c., rocks belonging to quite different groups. 

 Moreover, part of a dyke in accordance with this classification might be a mica-trap, 

 while the rest of it belonged to a different class, or, what is not imcomnion, the 

 margins of the dyke might be mica-trap, while the centre was doleryte or dioryte or 

 felstone or euryte or elvanyte. 



R. I. A. PKOC, SER. II., VOL. II., SCIKNCE. R 



