JET 9 



wood, and the transverse fracture, which is conchoidal, and has a resinous lustre, displays 

 the annular growth in compressed elliptical zones.' 



It does not appear to us that the ' ligneous origin ' of jet is by any means established 

 indeed, we think the amount of evidence is against it. There is no example, as far as we 

 can learn, of any discovery of true jet having a strictly ligneous structure, or showing 

 anything like the conversion of wood into this coal-like substance. There appears, 

 however, to have been some confusion in the observation of those who have written 

 on the subject. Mr. Simpson, the intelligent curator of the Whitby Museum, who 

 has paid much attention to the subject, says, ' Jet is generally considered to have 

 been wood, and in many cases it undoubtedly has been so ; for the woody structure 

 often remains, and it is not unlikely that comminuted vegetable matter may have 

 been changed into jet. But it is evident that vegetable matter is not an essential 

 part of jet, for we frequently find that bone, and the scales of fishes also have been 

 changed into jet. In the Whitby Museum there is a large mass of bone, which has 

 the exterior converted into jet for about a quarter of an inch in thickness. The 

 jetty matter appears to have first entered the pores of the bone, and there to have 

 hardened; and during the mineralising process, the whole bony matter has been 

 gradually displaced, and its place occupied by jet, so as to preserve its original form.' 

 After an attentive examination of this specimen, we are not disposed to agree entirely 

 with Mr. Simpson. 



Jet certainly incrusts a mass which has something the structure of a bone, but, 

 without a chemical examination of its constituents, we should hesitate even to say it was 

 bone. Wood without doubt has been found encrusted with jet, as fragments of animal 

 matter may also have been. But it is quite inconsistent with our knowledge of physical 

 and chemical changes, to suppose that both animal and vegetable matter would undergo 

 this change. "By process of substitution, we know that silica will take the place occupied 

 by carbon, or woody matter ; as, for example, in the fossil palms of Trinidad, and the 

 silicified forests of Egypt ; but we have no example within the entire range of the 

 coal-formations of the world of carbon taking the place of any of the earths. 



Jet is found in plates, which are sometimes penetrated by belemnites. Mr. Eipley, of 

 Whitby, has several curious examples, two plates of jet, in one case enclose water- 

 worn quartz pebbles ; and in another jet partially invests an angular fragment of 

 quartz rock. ' This is the more remarkable,' says Mr. Simpson, ' as quartz rock, or, 

 indeed, any other sort of rocky fragment, is rarely found in the upper lias.' 



The very fact that we find jet surrounding belemnites, casing adventitious masses 

 of stone, and investing wood, seems to show, that a liquid, or at all events, a plastic 

 condition, must at one time have prevailed. We have existing evidence of this. Dr. 

 Young, in the work already quoted, says : ' In the cavities of nodules containing 

 petrifactions, we sometimes meet with petroleum, or mineral oil. When first exposed, 

 it is generally quite fluid and of a dark green colour ; but it soon becomes viscid and 

 black, and at last hardens into a kind of pitch, which generally melts with heat, and 

 when ignited burns with a crackling noise, and emits a strong bituminous smell.' 

 One more sample of evidence in favour of the view that jet has been formed from 

 wood. It is stated (Seed's ' Illustrated Guide to Whitby') that in front of the cliff- 

 work of Hailburne Wyke existed a petrified stump of a tree, in an erect posture, 3 

 feet high and 15 inches across, having the roots of coaly jet in a bed of shale; whilst 

 the trunk in the sandstone was partly petrified, and partly of decayed sooty wood. 

 Even in this example it would appear, that after all, a coating of jet was all that 

 really existed upon this example of the equisetum, which probably stands where it 

 grew. Mr. Simpson, in a valuable little publication, ' The Fossils of the Yorkshire 

 Lias described from Nature, with a short Outline of the Geology of the Yorkshire 

 Coast,' says : ' From all we know respecting this beautiful mineral, it appears ex- 

 ceedingly probable that it has its origin in a certain bituminous matter, or petroleum, 

 which abundantly impregnates the jet-rock, giving out a strong odour when it is 

 exposed to the air. It is frequently found in a liquid state in the chambers of ammonites 

 and belemnites and other cavities, and, whilst the unsuspicious operator is breaking a 

 lias nodule, it flies out and stains his garment. This petroleum, or mineral oil, also 

 occurs in nodules which contain no organic remains ; and I have been informed by 

 an experienced jet-miner that such nodules are often associated with a good seam of 

 jet, and are therefore regarded as an omen of success.' 



Jet is supposed to have been worked in this country long before the time of the 

 Danes in England, for the Eomans certainly used jet for ornamental purposes. Lionel 

 Charltan, in the ' History of Whitby,' says, that he found the ear-ring of a lady having 

 the form of a heart, with a hole in the upper end for a suspension from the ear ; it was 

 found in one of the Eoman tumuli, lying close to the jaw-bone. There is no doubt 

 that when the abbey of Whitby was the seat of learning and the resort of pilgrims, jet 

 rosaries and crosses were then common. The manufacture was carried on till the time of 



