86 



ON SOME OF THE CRYSTALLINE LIMESTONES OP NORTH AMERICA. 



[1864 



of Lake Superior, specimens of which were shown in the exhi- 

 bition. 



Veins or lodes of sulphuret or carbonate of copper occur in 

 the lead region, particularly at Mineral Point, Wisconsin, where 

 they were formerly worked, but proved unprofitable ; and they 

 have been likewise found in Missouri. Metallic copper occurs 

 mainly in the trap rocks, and the copper ores, running through 

 sandstone and conglomerate, are not worked. Sulphurets and 

 carbonates of copper occur in the gold region of Virginia and 

 North Carolina, and in the same formation in Maryland. Na- 

 tive copper in large quantities is obtained from the trap rocks 

 of Lake Superior; and numerous mines have been opened 

 on the south shore of that lake. The copper is met with in 

 sheets of greater or less thickness, in vein cutting the trap 

 range nearly at right angles, and associated with various vein 

 fetones. These sheets of copper vary in extent, weighing from 

 a few pounds to 80 tons ; while the produce of copper from 

 the mines of Lake Superior during the past year will reach 

 4,000 or 5000 tons. A mass of native copper in the Exhibition 

 from one of these mines, weighed 6300 pounds; it was cut 

 from a mass weighing 40 tons, and the thickness between the 

 two natural surfaces was more than two feet. 



Aveinorbed of sulphuret of zinc, within the State of New 

 Yoi-k, has been somewhat extensively wrought. Zinc blende 

 often occurs with the lead ores, and the red oxide of zinc and 

 franklinite are found in New Jersy. The red oxide is largely 

 employed in the manufacture of the wliite oxide of zinc, and 

 the mixture of this ore with the franklinite, ground in oil in 

 its natural state, forms a brown paint much in use. The 

 franklinite has been of late successfully employed in a process 

 by which the ozide of zinc is obtained, and the iron reduced, 

 both operations being accomplished by the same furnace. Tin 

 ore (oxide of tin) has been found in New Hampshire, and it 

 also, in small quantities, accompanies the gold in Virginia and 

 North Carolina. 



Qtx some of tlie Crystalline Ijimestones of Nos-th America* 



BY T. S. HUXT, OF THE GEOLOGICAL COMMISSION OF CANADA.* 



The crystalline limestones of Canada, witli those of New York and 

 the New England States, may be divided into four classes, belonging 

 to as many different geological periods. The first and most ancient 

 occur in that sj'stem of rocks, named by Mr. Logan the Laurentian 

 series, which extending from Labrador to Lake Huron, forms the 

 northern boundary of the Silurian system of Canada and the United 

 States. The lowest beds of the Silurian repose horizontally upon the 

 disturbed strata of this oldest American system, a southern pro- 

 longation of which crosses the Ottawa near Bytown, and the St.- 

 Lawrence at the Thousand Isles, and spreading out, forms the moun- 

 tainous region of northern New York. This series consists in large 

 part of a gneiss, which is often garnetiferous ; but beds of mica slate, 

 qiaartz and garnet rock, hornblende slate and hornblcndic gneiss are 

 also met with, besides large masses of a coarsely crystalline, often 

 porphyritic rock, consisting chieiiy of a lime and soda feldspar, which 

 is sometimes labradorite, and at others andesine, or some related 

 species, and is generally associated with hypersthene. It often holds 

 beds or masses of titaniferous iron ore, and from its extent, occupies 

 a conspicuous place in the series. It is the hypersthene rock of Mc- 

 Culloch and Emmons. 



With these, the limestones are interstratified, but their relations to 

 the formation haye not yet been fully made out. All of these rooks 



* An Abstract of a paper read before the American Association for 

 the Advancement of Science, at Washington, April, 1854. 



bear evidences in their structure, that they are of sedimentary origin, 

 and are really stratified deposits, but their investigation is rendered 

 difficult by the greatly disturbed state of the whole formation. 

 Among these stratified rocks, there arehoweverdykes, veins, and masses 

 of trap, granite and syenite, often of considerable extent, which are 

 undoubtedly intrusive. Tliere are abundant eindences that the 

 agencies which have given to the strata, their present crystalline con- 

 dition, have been such as to render the limestone almost liquid, and 

 to subject it .at the same time to great pressure, so that in many 

 cases it has flowed around and among the broken, and often distorted 

 fragments of the accompanying silicious strata, as if it had been an 

 injected hypogene rock. 



The limestone strata are from two or three feet to several hundred 

 feet in thickness, and often present a succession of thin beds, divided 

 by feldspathic or siliciou.s layers, the latter being sometimes a con- 

 glomerate of quartz pebbles and silicious sand ; in one instance, 

 siriiilar pebbles are cont.iined in a base of dolomite. Beds frequently 

 occur in which the carbonate of lime has been mixed with silicious 

 sand, in some cases yielding an arenaceous limestone, while in others, 

 a chemical union has produced beds cf t.abular spar, often passing 

 into pjTOxene from an admixture of magnesia. These minerals some- 

 times form beds, in a nearly pure state, but in other cases they are 

 intermixed with quartz, carbonate of lime, orthoclase, scapolite, 

 sphene and other species. 



The limestones are sometimes coarsely crystalline, at others finely 

 granular or almost compact ; their color is white passing into reddish, 

 bluish, and grayish tints, which are often arranged in bands coincident 

 with the stratification. Some of the dark grey bands, harder than 

 the adjacent white limestone, were found by Mr. Murray to owe 

 their color to verj' finely disseminated plumbago, and their hardness 

 to intermingled grains of rounded silicious sand. The limestone is 

 often magnesian, and the manner in which the beds of dolomite are 

 interstratified with the pure limestone, is such as to lead us to sup- 

 pose that some of the original sedimentary deposits contained the 

 two carbonates, and that the dolomite is not the result of any subse- 

 quent process. 



The principal mineral species found in these limestones are apatite, 

 serpentine, phlogopite, scapolite, orthoclase, pyroxene, wollastonite, 

 idocrase, garnet, brown tourmaline, chondrodite, spinel, corundum, 

 zircon, sphene and graphite. All of these appear to belong to the 

 stratification, and the chondrodite and graphite especially, are seen 

 running in bands parallel to the bedding. Magnetic iron ore is some- 

 times found in beds interstratified with the limestone. The apatite 

 which is in general sparingly disti'ibuted, is occasionally very abun- 

 dant in imperfect crystals and irregular crystalline masses, giving to 

 small beds of the limestone the aspect of a conglomerate. Some of 

 the coarsely crystalline varieties of this limestone give a very fetid 

 odor when bruised. 



In some parts of this formation, in the rear of the bay of Quints, 

 the rocks are less altered than in most other places, and here the 

 limestones, although more or less crystalline in texture, afford none 

 of the fine crystalized species elsewhere met with. The foreign in- 

 gredients seem to be mechanically intermixed, giving an earthy appear- 

 ance to the weathered surface of the rock, or are separated in the 

 form of small grains of pyroxene, showing an imperfect metamor- 

 phism. For further descriptions of the rocks of this series, see the 

 Reports of the Geological Survey of Canada, particularly that of Mi\ 

 Logan for 1846, and Mr. Murray's for 1853; also Dr. Emmons's 

 Report on the Northern District of New York. In position and in 

 lithological characters, the Laurentian series appears to correspond to 

 the old gneiss formation of Lapland, Finland and Scandinavia. 



In the second class we include the crystalline limestones of western 

 New England, and their continuation in southeastern New York, and 

 the adjacent parts of New Jersey and Pennsylvania. The limestones 

 of the Champlain division of the Lower Silurian rocks which are 

 found on the Yamaska River, enter Vermont near Misisquoi Bay, 

 where they show a commencement of alteration. Farther south, they 

 become the white granular marbles of western Vermont, and of Berk- 

 shire, Massachusetts, which according to Hall, still exhibit upon their 

 weathered surfaces, the fossils of the Trenton limestone ; thence pass- 

 ing southwest, they cross the Hudson near AVest Point, and appear in 

 Orange and Rockland counties, New York, and in Sussex county New 

 Jersey, in a highly altered condition, closely resembling the crystal- 

 line limestones of the Laurentian series, and containing in great 

 abundance the same imbedded minerals. These limestones are some- 



