312 LADY McROEERT OX ACID AXD OTHER [Dec. 1914, 



A laro'e dyke extending across the Cauldshiels Loch is very 

 similar, and shows large, columnar, idiomorphic phenocrysts of 

 sanidine which can be picked out intact. These are carried in a 

 red ground-mass. 



Y. The Necks. 



The Chiefs wood neck is oval. Its larger diameter is a 

 mile and three-quarters long, and ranges north-east ; the smaller 

 measures three-quarters of a mile. 



It extends from Melrose well up into the moorland country, 

 about 700 feet above sea-level. It is in contact with Silurian 

 strata, except along its south-eastern boundary, where, as already 

 stated, Upper Old Ked Sandstone still remains. 



The materials of the vent are exposed in Huntly Burn and in 

 its three tributaries coming from the high ground on the south. 

 They consist here of decomposed yellow clay, well bedded near 

 the margin of the neck, and dipping inwards at about 30°. The 

 junction with the Silurian greywacke is clearly visible in Rhymers 

 Glen, about 20 yards below the lowest waterfall. 



There are plenty of quarries in the neck where fresh agglomerate 

 can be examined. The largest lies close to the railway-station, and 

 provides building- stone for Melrose. The agglomerate seen in 

 these quarries is a coarse accumulation of angular fragments up to 

 6 and 9 inches in diameter, with finer debris furnishing a matrix. 

 The fragments recognized were : — 



Silurian. 



Greenish and grey micaceous shales 



Grits and greywackes. 



Dark red sandstone. Old Red Sandstone . 



Flesh-coloured quartz -porphyry. 



Hard purple porphyry. 



Pink trachytes, similar to the Eildon trachytes. 



Amygdaloidal greenish basic glass. 



Olivine-basalt. 



The Little Hill neck is dealt with in this paper, on account 

 of its occurrence within the Eildon complex, otherwise its basic 

 constitution would exclude it from consideration here. The main 

 rock is a plug of fine-grained non-porphyritic basalt stained by 

 limonite, and often brecciated. This basalt consists of basic plagio- 

 clase, with fluxional arrangement and zoned with a fair proportion 

 of orthoclase and abundant olivine in small granules. 



An associated rock at the western end of the hill is closely allied 

 to the Markle type of basalt. Phenocrysts of basic labradorite 

 (60 to 70 per cent, anorthite) and decomposed olivine lie in a 

 ground-mass of labradorite-laths associated with much limonite. 

 On the two sides of a wall at the western end of this composite 

 plug an ash occurs, containing small fragments of basalt, trachyte, 

 greywacke, and shale. Small dykes are seen penetrating the ash 

 from the adjoining plug. 



The Little Hill neck is bounded on the west by sedimentary rocks 

 of Silurian age, but on the north is in contact with a narrow band 



