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 PROM PHIVATE COLLECTIOJfS . 
(By the Editor and his Friends.) 
I.— AMMONITES COMMUNIS ; FROM THE LIAS OF WHITBY, 
YORKSHIRE. 
In 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. 
I^or is Whitby wanting in historical associations. It was there, in 
Anglo-Saxon days, stood the far-famed monastery of Streones-healh, of 
