VEGETABLES. 189 



pyritous, or calcareous, and another pure jet; or even one part 

 preserved vrood, while another is real jet. Sometimes a crust of 

 excellent jet, an inch thick, is found on the outside of a log of 

 pyritous or siliceous wood. Even the pieces of jet which occur 

 by themselves all betray their ligneous origin. They are in the form 

 of flattened branches or trunks of trees ; or compressed fragments, 

 like pieces of the common petrified wood ; and the outer surface 

 is always striated with longitudinal markings, like the grain of wood, 

 while the transverse fracture, which is conchoidal with a resinous 

 lustre, displays the annual growths in elliptical zones ; which are 

 more or less flattened, according to the degree of compression 

 which the wood has undergone. The same facts are also exhibited 

 in the longitudinal fracture. Besides, we often observe branches 

 diverging from the principal mass ; and on taking up such specimens, 

 their bed is found to be the exact impression of the trunk of a tree 

 with its branches. The larger masses are about ten or twelve feet 

 long, eighteen or twenty inches broad, and only from an inch to two 

 inches thick. Their great flatness is a striking peculiarity. It would 

 seem that, by one of those processes which have been carried on in 

 nature's laboratory, the wood imbedded in the strata has been 

 reduced to a soft pulpy state, and in that state has been compressed 

 into flat pieces by the weight of the superincumbent mass. The flat 

 surface, as might be expected, is generally parallel to the plane of 

 the strata; which is also the case with the flat pieces of common 

 petrified wood, especially the larger specimens, and even with most 

 of the petrified plants. When a core of siliceous wood remains 

 within the block of jet, it is only partly flattened; the silex having 

 obstructed the natural process. 



The electric property and beautiful black lustre of jet are well 

 known. Within these few years, great quantities of it have been 

 manufactured at Whitby and Scarborough into ornaments and trinkets 



3 A 



