CHARACTER 0E THE WHEN" SELL OE NORTHEMBERLAISTD. 417 



Farms near Bavington ; West Whelpington, Elf Hills, Shield Dykes, 

 St. Margarets, Ratcheugh, and abundantly in the districts further 

 north. 



Fragments of altered rock are frequently found in the Whin. 

 We cannot say whether these fragments belong to beds lying above 

 or below ; and therefore the fact of included sedimentary strata 

 proves nothing. But the condition of the fragments is important 

 evidence : they are pieces of shale or sandstone, not irregular amor- 

 phous masses such as would have occurred if the Whin had been 

 poured over the ocean-floor and had caught up patches of newly 

 deposited sediment in its progress. The shale immediately over the 

 Whin, although greatly altered, is sometimes highly fossiliferous. 

 This could not have been the case had the clayey sediment been 

 laid down over freshly ejected lava. 



The altered shale is frequently known as " Whetstone," a term 

 also in use in Scotland for similar beds. When the shale can be 

 used as slate-pencil it is known as " Cam ;" Camboe, near Elf Hills, 

 is by some supposed to derive its name from this circumstance. 



Altered sandstone often greatly resembles altered or partly de- 

 composed Whin. The surfaces of the Whin are frequently altered 

 by the rocks it traverses quite as much as the rocks are altered by 

 the Whin. This mutual metamorphism, or alteration, is even 

 better shown by the Whin Dykes * than by the Whin Sill. 



The Whin Sill frequently rises up in bosses of bare rock from a 

 drift- covered country. Where there is no drift, or only a thin and 

 partial covering, it generally forms the main feature of the imme- 

 diate district in which it occurs. Its escarpment is not so lofty 

 as that of the thick sandstones, which chiefly lie on lower horizons ; 

 but it is usually more bold and precipitous in proportion to its 

 height. The Whin Sill can frequently be distinguished at a dis- 

 tance by the character of the vegetation. Mr. Tate states that the 

 following plants occur in Northumberland only on the basalt — 

 Moenchia erecta, Sagina subulata, Vicia lathyroides, Asperugo pro- 

 cumbens, St-Jtice limonium, Convallaria polygonatum, Allium schamo- 

 prasum, Scilla verna, Seclum anglicum, Asplenium septentrionale, 

 and A. germanicum. Helianthemum vulgare, although also occur- 

 ring on the limestone, is very characteristic of the Whin Sillf. 



5. Mineral Characters of the Whin Sill. — Into this subject we need 

 not enter, inasmuch as Mr. Allport has quite recently done so at 

 length before this Society. Of the specimens described by him J two 

 were from our district. That from Ward's Hill is a good typical 

 example of the Whin Sill generally. That from Elf Hills was from 

 one of the small strings of trap shown in fig. 2 (p. 413). It is by no 

 means a fair example of the trap, being excessively fine in grain, 

 almost resembling a hardened clay ; it is moreover much decomposed. 



* It may be well to mention that faults in the N. of England are called 

 " dykes " or " troubles." Basaltic dykes are specially distinguished as " Whin 

 dykes " or " Whin troubles." 



t New Flora of Northumberland and Durham, p. 35, 1868. 



I Quart. Journ. Geol. Soc. vol. xxx. p. 552, 1874. 



Q. J. G. S. No. 130. 2 e 



