ALTERATION OP COAL THROUGH CONTACT. 53 



amined by them in 1874. Those observers regard the change as due to 

 the influence of eruptive rocks. ' 



Examples of Contact-alteration in Virginia and N^orth Carolina. — The well- 

 known conditions in the coal-fields of eastern Virginia and of North 

 Carolina render those areas equally illustrative. Dikes passing across 

 the coal in Virginia have changed it in many places into coke, which at 

 one time was sold in eastern markets under the name of James river 

 carbonite. Anthracite has been formed under similar circumstances at 

 some localities in North Carolina. 



Examples of Contact-alteration in New Zealand. — Dr Haast^ made many 

 references to the occurrence in New Zealand of coal altered by contact 

 with dolerite; sometimes coked, at other times changed wholly into 

 anthracite. In the same report Dr Haast tells of the Hesse Cassel brown 

 coals, altered by basalt sheets, which in man}^ cases form both roof and 

 floor of the seams. Occasionally, Avhere the flow was small, the effect is 

 insignificant. The mode of change is well exhibited near the Meissner, 

 where the mines have been worked for two hundred years. The seams, 

 for the most part, are from 20 to 30 feet thick, and are changed only in 

 part. The effect of the heat extends from 7 to 17 feet, according to the 

 thickness of the overlying l)asalt. Immediately below that rock, for 

 from 1 to 4 feet, the change into anthracite is usually complete, but 

 thence downward the passage is gradual to the wholly unchanged brown 

 coal. Dr Haast describes a condition very like that observed in our own 

 Placer field, a coal-bed in contact with a dolerite dike is changed into 

 anthracite, but the change becomes less as distance from the dike in- 

 creases, until the normal '' pitch coal " is reached. Dr Hector in the 

 same report adds some interesting notes f to Dr Haast's observations. 



Alteration through Contact not invariable. — While it seems to be suffi- 

 ciently clear that bituminous coal can be converted into anthracite by 

 the agency of heat, it must be remembered that there are localities 

 where intrusions of lava have been without influence, and that there are 

 others where, as will be shown, notable folding and crushing have been 

 ineffective, and that there are others where close proximity to granite 

 and other crystalline rocks has led to no change. 



OBJECTIONS TO ROGERS'S HYPOTHESIS. 



Two fundamental assumptions in the hypothesis off'ered by Professor 

 Rogers are erroneous : First, that anthracite is necessarily due to meta- 

 morphism, and, second, that the plication of the Appalachian region was 



*nuast: Geol. Survey of New Zealand; Reports of geological Explorations during 1871-'72, pp. 

 51, 52, 54, 82. 

 t Hector: Loe. eit., p. 147. 



