110 



THE GEOLOGIST. 



trap properly so called, are often found in contact with lignite, coal, 

 anthracite, and even graphite. In these cases metamorphism has 

 sometimes been very feeble or null. In the Giant's Causeway a sheet 

 of trap has overspread a bed of lignite without causing the slightest 

 alteration in the structure or aspect of this substance. Such extra- 

 ordinary examples as this are, however, very rare, and require eluci- 

 dation. 



Generally speaking, the contact of trap-rocks either renders the 

 combustible more compact, or changes it into a species of coke. In the 

 former case lignite becomes coal, anthracite, and sometimes graphite. 

 "When any combustible has been thus modified by the presence of 

 trap-rock, it is observed to have taken a prismatic structure in those 

 parts which are immediately in contact with the eruptive rock. M. 

 Delesse has observed this curious fact in lignite, coal, anthracite, and 

 also in graphite. 



This prismatic structure is very difficult to explain, and is rendered 

 the more so by the fact that samples presenting it shrink still more when 

 they are artificially heated, evolving, at the same time, water and 

 volatile bituminous matter, and becoming genuine coke. 



We shall refer again to other observations on metamorphism made 

 by M. Delesse. We have dwelt on the foregoing more particularly as 

 they contain a few facts confirming ideas that we ourselves have 

 cherished for many years, and which embrace some of the most in- 

 teresting geological phenomena. We will endeavour to lay them 

 before our readers at some future period, which we hope may not be 

 far distant. 



GEMS FROM PRIVATE COLLECTION'S. 



(By the Editor and his Eeiends.) 



L— AMMONITES COMMUNIS ; FROM THE LIAS OF WHITBY, 

 YORKSHIRE. 



lu the Collection of J. S. Boweebank, Esq., F.R.S., F.G.S,, &c. 



At the extremity of a pretty bay, on the coast of Yorkshire, stands 

 the town of Whitby, known to every geologist for the numerous 

 treasures of organic remains which the Lias beds, there outcropping on 

 the shore, have furnished at various times. 



Nor IS Whitby wanting in historical associations. It was there, in 

 Anglo-SMxxon days, stood the far-famed monastery of Streones-healh, of 



