Frof. W. King — On the Structure of a Rock from Ceylon. 19 



are also in some specimens traces of oxide of copper. The lead, 

 which is more abundant than at Huntington, occurs in the form of 

 ordinary galena or sulphide of lead, but so far no other ore, except 

 manganese and ii'on, have been detected, although it is most pro- 

 bable that both cobalt and nickel, and possibly tin, may exist in 

 small quantities. 



With regard to the origin of these ores, or under what condition 

 they were produced, I will not here venture an opinion. I believe 

 they determine the lines of some important disturbance ; but, how- 

 ever this may be, their occurrence at these particular and widely 

 separated points is certainly curious, and worthy of investigation, and 

 probably other sinkings in the conglomerates of the Chase will help 

 to throw some light on the subject. How far they extend down- 

 wards in the conglomerates the present sinkings will of course 

 determine; in August last, they had not been met with below 

 108 feet from the surface, but copper made its appearance much 

 lower down. Tlie Coal-measures I believe will be struck at about 

 240 feet from the surface, and I should not be surprised to 

 find these ores mixed up more or less with the gravel and sand- 

 stone down to their base. I may remark that copper ore of this 

 description occurs in Permian rocks near Barlaston and Trentham, 

 and at other places in North Staffordshire, and it is also found in 

 large quantities associated with lead, cobalt, and other commercial 

 ores, in Keuper sandstone, at Alderley Edge, in Cheshire; but I 

 myself am not aware that at any other locality than Cannock Chase 

 have copper and lead ores -been found in undoubted Bunter con- 

 glomerate in England. I do not in their present form, and in the 

 face of richer deposits, attach much commercial value to them ; but 

 geologically they are of much interest, and it is these circumstances 

 which have led me to publish the few facts I have been able to 

 obtain in reference to them. 



VI. — The Microscopic Chakacters of a Silo-oarbaoid Eook 

 FROM Ceylon ; and their Bearing on the Methylotic Origin 

 of the Laurentian " Limestones." 



By William King, Sc.D., Professor of Mineralogy and Geology in Queen's 

 College, Galway. 



THE rocks usually called metamorphic ^ may be conveniently 

 divided into two great groups — Silacids and Silo-carbacids, 



^ The term metamorphic is herein restricted to rocks that have hecome structurally 

 changed or mineralized. 1 propose the term niethylosis (from nieta, chiiiige ; and hyl, 

 substance) to express the various oAe/wica/ changes which certain rocks have undergone 

 since their formation by eliminations of. or additions to (both processes acting simul- 

 taneously, or one alone) tlieir original substances to a nmre or less extent The changes 

 are analogous to those of pseudomorphism in minerals. This last term has occasionally 

 been applied in the case of rocks ; but some have, with much reason, urged that it 

 ought til be confined, as originally understood, to chemical changes in cr\ stals unaccom- 

 panied by any alteration of their form A term similar to meihylosis (but 

 coming from different roots) is in use among chemists: geologists, however, are not 

 likely to confound the two. Methylotic rocks, I feci persuad^■d, will prove to be 

 commoner than appears to be known. They are not altogether contimd to meta- 

 morphic associations; as some — such as coal, magnesiau limestoues. diloritic, and 



