412 W. TOPLEY AND G. A. LEBOUR ON THE INTRUSIVE 



stone. From this point the Whin Sill trends almost due north in 

 a fine line of semi-columnar crags as far as Knowes Gate, where it 

 crosses the Wansbeck-Valley Railway. This portion of its course 

 is twice interrupted by surface breaks unattended by change of 

 horizon, at Sweethope and at the Berry Hills. At Knowes Gate 

 this long basaltic range terminates abruptly, reappearing at intervals 

 through a drift-covered country. Parallel to this great ridge, how- 

 ever, and not quite a mile to the east of it (three beds of limestone, 

 with their associated sandstones and shales intervening), is another 

 equally thick (and in places even thicker) but much less regular 

 Whin Sill, which we will call the Eastern Branch, and which runs 

 from Homilton, near Bavington, to Elf Hills, to the N.E. of Kirk- 

 whelpington (see fig. 1). This eastern basaltic sheet is much more 

 subject to breaks than the western one, and towards its northern 

 extremity comes to the surface usually not as a continuous bed, but 

 in bosses or isolated masses of greater or less size. 



At Elf-Hills Quarry, where the Four-fathom, or Saccammina-Lime- 

 stone* was until lately wrought, the Whin overlies and breaks 

 through the limestone. But a more interesting case of intrusion 

 was observed by Sir W. Trevelyan a few years back, which is illus- 

 trated by fig. 2, from a sketch by us, taken at the time : a thin 

 layer of fine-grained Whin underlies the limestone and sends up 

 strings of trap through the overlying beds. 



To the north of Elf Hills there is a broad flat tract of drift-covered 

 land, beyond which the Whin is again seen (at Hartington and 

 Gallow Hill) lying in the same position as the main bed at Elf 

 Hills, between the Great and Four-fathom Limestones. Again 

 there is a broad drift-covered valley, beyond which the Whin is 

 seen at Dike Head. It here seems to come up as a great boss, and 

 lies lower in the series than at Elf Hills. A borehole put down 

 on the south of Greenleighton Farm found the Whin just below the 

 Six-yard Limestone ( = Three-yard Limestone of Teesdale). 



In Fallowlees Burn the Whin lies about 100 feet below the posi- 

 tion last mentioned. From this place it can be traced for about a 

 mile to the north, apparently keeping at the same horizon. 



At Wards Hill (fig. 3) the W T hin lies above the Great Limestone. 

 A little below the Great Limestone there is a seam of coal which has 

 been a good deal worked over the north-eastern part of the hill. 

 At one pit the coal was followed for some distance under the Whin, 

 where it was found to be gradually deteriorating and at last was 

 quite caked and worthless. The Whin has then evidently cut 

 through the limestone and has here reached the coal. This is also 

 evident from the surface-mapping ; for on the south-east face of the 

 hill the limestone occurs above the Whin, and on the south-west 

 the Whin certainly cuts through the beds, passing through the 

 Great Limestone and the beds below, and at last underlying the 

 coal, which lies about 40 or 50 feet below the Great Limestone. 



The W T hin is not seen again until we reach the hill N. of Shield- 



* Through Northumberland, as far north as the river A In, Saccamina 

 Carteri, Brady, appears to oocur chiefly in the Four-fathom Limestone. 



