ECONOMIC GEOLOGY. 31 
■ocks in the Cranberry quadrangle which he considers pre-Cambrian. These porphyritic 
■ocks have likewise been regarded as pre-Cambrian by others." 
From all the facts available it seems most reasonable to regard these rocks, and the 
netamorphism which affected them, as probably of pre-Cambrian age. While a more con- 
clusive statement can not now be made, the writer believes that later detailed study will 
confirm this view. 
IGNEOUS ROCKS. 
The igneous rocks which are now represented by granitic gneiss and amphibolite first cut 
he sediments and then were metamorphosed with them. The massive granite, some of the 
>egmatite, and the diabase are later than the metamorphism which formed the schists and 
,re of course older than the planation of the region, which probably took place in Tertiary 
ime. As has been stated, Paleozoic granite is not known in the South, and the granite and 
>egmatite are therefore probably pre-Cambrian. It has been shown on page 20 that 
he granite intrusion probably marked the end of the metamorphism; and this furnishes 
,nother evidence in favor ot the belief that the great movements resulting in metamorphism 
ook place in pre-Cambrian time. The porphyries and volcanic tuffs are likewise considered 
o be of pre-Cambrian age, appearing probably near the close of the metamorphism. 
The diabase dikes are certainly the youngest of the igneous rocks, and have certainly 
scaped regional metamorphism, but more definite evidence as to their age was not obtained 
n this area. The writer is informed by the State geologist of South Carolina, Hon. Earle 
>loan, that the diabase cuts Juratrias sediments and is probably of that age. 
SEDIMENTARY ROCKS. 
The comparatively small amount of induration, alteration, and contortion of the sedi- 
nents occurring in the vicinity of Monroe, N. C, has alread}^ been described. It is difficult 
o believe that these soft rocks could have been present when metamorphism of the schists 
ook place. On the other hand, they are older than the Triassic deposits of the "Newark" 
ystem. Fossils have not yet been found in the "Monroe" beds and their age remains a 
[latter of uncertainty. The sands of the Coastal Plain formation which are included in this 
rea are regarded by Doctor Sloan as probably belonging to the Columbia group of the 
Quaternary. 
ECONOMIC GEOLOGY. 
In the number of its mineral species North Carolina is said to excel any other State in the 
Jnion, and a great variety of .minerals has been found in South Carolina. These minerals 
ave long been prominent among the resources of the Carolinas, and the particular area 
escribed in this report has been one of the important localities in this respect. 
Mining in this general region dates back before the time of the settling of America, and 
arly Spanish and English accounts of the discovery and recovery of metals are numerous. & 
"he principal mineral resource of this Carolina area is gold. Iron has been mined to a con- 
iderable extent, and within recent years the monazite industry has attained some impor- 
ance. Tin is now creating considerable excitement. Besides these materials, copper, lead, 
langanese, pyrite, mica, barite, corundum, clay, limestone, and granite are or have been 
aund and worked to a greater or less extent. 
TIN. 
The use of tin is steadily increasing and the demand for it is constantly growing. While 
iew localities are being discovered from time to time, and while certain of the districts 
Iready known are increasing their output, some of the important tin-producing regions of 
he world are on the decline and others do not give promise of long maintaining their present 
a Williams, G. H., Jour. Geol., vol. 2, 1894, pp. 28 et. seq. Becker, G. F., Gold fields of the Southern 
Lppalachians: Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 3, 1895, p. 260/ 
&Cf. Becker, G. F., Gold fields cf the Southern Appalachians: Sixteenth Ann. Rept. U. S. Geol. 
urvey, pt. 3, 1895, pp. 253-257. 
