Mr. Williamson Peile's Description of a Group of Dykes. 163 



lowing, however, the direction of the main body of the Rider, as shewn 

 by the section. 



The insulated large pieces of Coal were perfectly free internally 

 from any mixture with the stone, but the small pieces on the right 

 hand (of which specimen No. 4 is one) presents so singular an ap- 

 pearance as almost to tempt me to call on Mineralogy, for a new appli- 

 cation to the term Plum-pudding Stone, to convey an idea of the very 

 great mixture. 



I have nothing to add to the section No. 2., the substances were 

 the same, and their situation is well represented. 



These Riders were not first discovered in the Main Band, but were 

 found in the workings of the Bannock Band, a seam which there lies 9 

 fathoms above the other, and which workings proved the course of the 

 Riders very accurately. Some time afterwards when the Main Band 

 was wrought underneath, we were surprised to find that they existed 

 also there, bearing the same features as in their higher position, and 

 directly under the other ; thus shewing the exact perpendicular course 

 they have preserved in their passage through the strata. And since 

 we have thus found them in two seams, without a limit to their course, 

 appearing either in the roof of the higher, or thill of the lower seam, 

 it is fair to infer the probability of their cutting all the strata of 

 the Coal formation from the surface to its lo west member. It must 

 be admitted that a different idea might be countenanced by an inspec- 

 tion of the section, viz. that they have darted at several intervals from 

 the Upcast Dyke, perpendicularly into the strata, and it is further evi- 

 dent from the position of the Black Metal Stone in the profile, that 

 the passage of the Dyke has been downwards ; but to correct this, I 

 must add that the section is not laid down to an accurate scale, and 

 was intended merely to simplify the description of the Dykes. Pro- 

 bably the hade of the upcast is much less than represented — and the 

 distance from it to the Riders is contracted in the section. 



The Riders, in general, but not always, throw the seam a few inches 

 out of its level, the upcast being to the eastward. The great parallelism 



