310 LADY McROBERT OX ACID AND OTHER [Dec. 1 9 Mr 



likely that nepheline will he found in this type than in any of 

 the others met with in the Eildon Hills, but as } r et neither micro- 

 scopic examination nor staining has revealed any. 



Bowden Moor Quarry. — Near Bowden Moor, half a mile due 

 west of Eildon Wester, is an oval, grass-covered mound, of which 

 almost the Avhole interior has been quarried away. The quarry 

 yields a fine-grained, pink, compact trachyte, showing scattered 

 small sanidine-phenocrysts, generally decomposed. These lie in a 

 trachytic ground-mass of sanidine-laths, with a certain amount of 

 primary interstitial quartz, sometimes enclosing the laths ophitically. 

 Secondary quartz is abundant in small vesicles. Limonite, in 

 spongy aggregates and large masses, possiblv represents original 

 riebeckite. The rock, as a whole, resembles the trachyte of the 

 spur extending westwards from Eildon Wester Hill. 



The Whitelaw Hill Sill lies about a mile and a quarter 

 south-west of the above, and is petrologically so similar that it 

 does not require description. It forms the oval cap of the hill, its- 

 longest diameter being about 10 yards. It is in contact with 

 Silurian shales and greywackes, except on its south-east side, where 

 a coarse yellow grit is found, which Mr. Pringle attributes to the 

 Upper Old Bed Sandstone. The north-western boundary is a black- 

 banded flinty rock with conchoidal fracture, which extends for 

 some distance beyond the present position of the trachyte. It 

 would seem to be a fine-grained shale, intensely indurated by 

 silicification subsequent to the intrusion. The mass appears to be 

 in connexion with a dyke which runs south-eastwards from the 

 hill- top. 



IV. Dykes. 



The dykes of the district nearly all run in a general north- 

 easterly direction ; it is certain that many of them belong to the 

 same suite of intrusions as the laccolites and sills just described, 

 but it is possible that some may date from the Lower Old Bed 

 Sandstone period of igneous activity. 



The field-evidence bearing upon the point is as follows : — Two 

 trachyte-dykes of rather irregular form cut the Upper Old Bed 

 Sandstone north-west of Earlston. Two others are met with in 

 the narrow strip of the same formation bordering the Chiefswood 

 neck, while a quartz-porphyry dyke is found actually within this- 

 neck. A large trachyte-dyke forming Cauldshiels Hill, though in 

 the main traversing Silurian strata, cuts across a small outlier of 

 the Upper Old Bed Sandstone immediately south-east of the old 

 fort. 



The group of three dykes, half a mile south-west of Cauldshiels- 

 Hill, has been found to consist of riebeckite-trachytes, wherefore 

 their connexion with the Eildon suite of intrusions may be taken 

 for granted. 



