550 MESSRS. HILL & KYNASTON ON KENTALLENITE [Aug. I 900, 



varieties. Thus in Glen Strae occurs another basic lamprophyre 

 [5539], which does not show nearly so high a proportion of augite 

 as the rock above described ; while brown hornblende has mad© 

 its appearance, and exhibits the elongated prisms characteristic of 

 camptonite. Again, a sill occurring 1 mile north of Craig House, 

 Dalmally [8459 & 8615], is a fairly typical camptonite, which appears 

 only occasionally to contain augite in the more basic portions of the 

 sill [8459]. Similar camptonites, without augite, and various closely- 

 related hornblende-lamprophyres are common in the Glen-Orchy 

 area [8677, 8678]. Thus the Ben-Cruachan area also furnishes 

 strong evidence of the close relationships between our more basic 

 lamprophyres and the augite-diorites with affinities to kentallenite 

 on the one hand, and the camptonites on the other hand. Similarly 

 we might describe transitional varieties between the hornblende- 

 lamprophyres and the porphyrites, the numerous sills of which are 

 so characteristic a feature of both the Ben-Cruachan and Glen- 

 Pyne areas ; and there can be no doubt that these porphyrites 

 represent the dyke- or sill-phase of the larger masses of horn- 

 blende-granite. In short, the evidence afforded by the occurrence 

 of these numerous connecting varieties enables us to bind an 

 assemblage of intrusions, consisting of a large number of rock-types,, 

 into one connected whole. 



Before leaving the lamprophyres, we would refer briefly in 

 this connexion to the sill, described on p. 546 as augite -diorite r 

 on Meall-an-Laoigh, near the head of Glen Strae. While the 

 main mass of this sill may fairly be referred to augite-diorite, 

 the central portion consists of a hornblende-lamprophyre of a type 

 by no means common in this district. The passage between the 

 two kinds of rock is somewhat sudden, yet the lamprophyre can 

 scarcely be regarded as a distinct intrusion, as it has no fine-grained 

 margin, and the characteristic idiomorphic augites of the dioritic 

 type are still seen to occur, though less abundantly. The lampro- 

 phyre frequently veins the diorite in an intricate manner, and the 

 two types are often so intermingled, that they cannot be otherwise 

 regarded than as portions of the same mass. 



A section of the lamprophyric type is seen under the microscope 

 [8946] to consist mainly of elongated prisms of greenish-brown 

 hornblende and alkali-felspar. The hornblende is of the same type 

 as that so characteristic of many of the camptonites of the same 

 area. The alkali-felspar constitutes a granular aggregate, forming 

 as it were a background in which the hornblende-prisms lie em- 

 bedded. Occasionally a larger patch of hornblende is seen to con- 

 stitute a pseudomorph after augite. There is some plagioclase, but 

 the orthoclase is largely in excess. Sphene and apatite are accessory, 

 the former being of the same variety as that found in the augite- 

 diorite. The rock apparently belongs to the syenitic lamprophyres, 

 and since it consists essentially of alkali-felspar and hornblende, 

 may be referred to vosgesite. The intimate association of these 

 two types of rock in one mass leaves no doubt as to the close 

 genetic relationships between the augite-diorites and the lampro- 



