1866.] MEETING OF AMERICAN ASSOCIATION. 123 



strata holding coal and pyroschists was exposed; and it was 

 remarked, among arguments founded upon the impermeability of 

 many of the petroleum-bearing strata, that the oil of the Trenton 

 limestone occurs below the horizon of any pyroschists, or other 

 hvdrocarboneous rocks. 



A discussion on the subject of Petroleum followed, in which 

 Dr. Andrews, Prof. Hall and Prof. Newberry took part. 



ON THE LAURENTIAN LIMESTONES AND THEIR MINERALOGY. 



BY DR. T. STEKRT HUNT, F.R.S. 



The author alluded to the existence in the Lower Laurentian 

 system of three limestone bands or formations, of great but 

 variable thickness, which might fairly be compared with the great 

 limestone groups of the North American paleozoic system. In 

 addition to these, there is probably a fourth and newer limestone 

 formation belonging to the lower or true Laurentian, besides one 

 or more in the unconformable overlying Labrador series or Upper 

 Laurentian. The three limestone formations first named are 

 separated by great masses of gneissic and quartzose strata, and 

 are intimately associated with beds in which silicates of lime and 

 magnesia prevail, together with graphite, and various metallic 

 ores. The minerals associated with these limestones, and their 

 accompanying strata, were next considered, and it was shown that 

 they occur, both disseminated in the beds, and filling fissures or 

 veins which traverse the strata. The importance in a geological 

 point of view of these veinstones, which from their mode of 

 formation might be named endogenous rocks, was insisted upon. 

 They may attain very great dimensions, and may include any or 

 all of the mineral species belonging to the adjacent stratification, 

 variously grouped, and sometimes, having a banded arrangement 

 parallel to the walls of the vein. Among the characteristic 

 minerals of these veins are calcite, apatite, pyroxene, hornblende 

 serpentine, chondrodite, orthoclase, scapolite, phlogopite, quartz, 

 garnet, idocrase, epidote, spinel, corundum, sphene, zircon, mag- 

 netite, and graphite. Some of these occasionally occur in a nearly 

 pure state, filling the veins, as graphite, pyroxene and apatite. 

 Veins of crystalline carbonate of lime, generally including some 

 one or more of the preceding minerals, are often met with, and it 

 is these which have given rise to the notion maintained in this 

 country by Emmons, and in Europe by Leonhard and others, that 



