FOREIGN CORRESPONDENCE. 



161 



on the Organization of Trilobites," called it Fhacops caudatus, which 

 generic determination modern palaeontologists have followed. 



One of the chief features in the species is the great prominence of 

 the eyes and the distinctness of the numerous lens-facets into 

 which those special organs are divided. 



There are certain variations in the outlines and form of this, as 

 well as of other species of Trilobites, which have been regarded by 

 naturalists as sexual characteristics ; judging upon these grounds, 

 Mr. Tennant's specimen would be probably considered a female. 



This species, Phacops caudatus, ranges in vertical stratigraphical 

 distribution from the Lower Llandeilo flags to the Upper Ludlow 

 rock, and it has also a considerable geographical range. 



The species has been described at length by Burmeister, and also in 

 the Decades of the Geological Survey. 



FOREIGN CORRESPONDENCE. 



By Dr. T. L. Phipson of Paris. 



On the Crystalline form of Coal — Coal and Carhureited Hydrogen in 

 Meteoric Stones — Coal that cuts Glass like the Diamond — Another 

 word on the Artifcicd formation of Coal. 



I HAVE just published in France some observations " On the Crystalline 

 form of Coal.""^ In November, 1858, I picked up in London some 

 fragments of coal that were perfect rhomhohedrons, giving angles of 

 102° and 78°. This coal came from Sunderland. In December fol- 

 lowing I found many analogous specimens near the town of Glasgow, 

 in Scotland, one of which measures nearly a foot in every direction. 

 The coal-beds near Glasgow have been upheaved by trap-rock, and the 

 immense pressure has given to the coal a crystalline structure that 

 causes it to break under the hammer in rhombohedric fragments ; 

 and these, whatever be their size, give always the same angles, 102° 

 and 78°. Graphite, which is known to be a variety of pure carbon, 

 is found crystallized in short hexagonal prisms (laminae), that is, in a 

 form derivable from the rhombohedron. Coal and graphite belong 

 therefore to the same crystalline system. This fact goes a long way 

 to prove that coal must be regarded as a variety of pure carbon, and 

 not as a combination of carbon, hydrogen, oxygen, and azote, as some 

 have asserted. For the oxygen, hydrogen, and azote that coal gives 

 on analysis are derived from the siibstances, such as bitumen, naphtha, 

 vegetable remains, &c. with which it is mixed. 



* Bulletin de la Soc. d'Hist. Nat. dc Strasbounj, and Journal de Pharmacotogie 

 de BruxcUcs. 



