Fig 5-Group of drill-hole sections near Dɔe Run, illustrating variability of stratification. Other drilling done south of this, in section 18, revealed the same general conditions as are expressed in the following notes: The most important general conclusions to be derived from the study of these sections, are that the upper members are uniformly beds of magnesian limestone, of varying texture and color, while the lower members are generally sandstone, or arenaceous limestone; that beds of shale are sometimes found above these lower sandstone beds, and that beds of sandstone exist in places higher up in the section, between two limestone strata, that but such beds are not constant. Proceeding westward from Doe Run, we pass over the great area of crystalline rocks included in Stono mountain and the surrounding country. Thence west of Stono postoffice in the valley along the turnpike to Iron Mountain, a coarse, friable sandstone is encountered at several places. It is the lower member and remnant of a series of sedimentary beds which once existed in estuary like-deposits between the surrounding hills. Such sandstone is exposed near the road about two miles west of Stono postoffice. It occurs on both sides of the road leading to Bismarck, between Pine mountain and the opposite spur of Stono mountain. It is well shown at the toll-gate at the northern end of Pine mountain, being exposed in ledges on both sides of the road. The rock here is very impure, coarse and gritty, being composed of grains of sand as much as one-tenth of an inch in diameter, and includ ing pebbles of decomposed porphyry; much clayey material, resulting from the decomposition of porphyry, is also disseminated through the matrix of the rock, making it soft and friable. It is of a buffish yellow color. Between Pine mountain and the northern extension of Iron mountain, similar sandstone crops out. At one place, at the forks of the road, about the middle of section 20, the rock is a decided conglomerate, consisting of small pebbles of sub-angular quartz, and of larger and more rounded porphyry fragments, cemented by a clayey matrix of decomposed porphyry. It is a soft, friable rock, and lies close upon the porphyry floor. Iron Mountain and Vicinity.-Passing from this to Iron Mountain, we have exposed in the excavations of the mine at that place beds of limestone and sandstone which taper to a feather edge up the mountain sides. These are well exposed in the cut on Little mountain, at the western end of the mine. The face here includes yellow, friable sandstone, 40 or 50 feet thick, overlying a bed of magnesian limestone, about 15 feet thick, which reposes directly upon the porphyry. 2 5 Fig. 6. Cross-section through Little mountain open cut at Iron mountain. 1. Surface clay and detrital ore. 2. Paleozoic sandstone. 3. Paleozoic dolomite. 4. Pre-Paleozoic clay and detrital ore. The relations of the rocks here are well shown in the adjoining section. The results of drilling about the mountain show, however, that this succession and relation of the rocks is not constant. Some ten or more churn drill holes have been put down in the valley along the foot of the mountain. The samples of the drillings are preserved by the Iron Mountain company, and were examined by the writer. The positions of these holes are exactly shown on the map of the mine accompanying the description of the iron ores, later in this report. The following descriptions of the rocks encountered are from the writer's study of the samples, and from the records of the drilling prepared by Prof. Potter: Section IV (No. 4 of Section sheet). RECORD OF IRON MOUNTAIN DRILL-HOLE NO 17. FT. IN. 1. Clay... 2. Black mud.... 3. Limestone, light gray, highly arenaceous, almost a sandstone. 4. Limestone, brick-red, slightly arenaceous... 5. Sandstone, grayish-red, coarse-grained, strongly effervesent..... 9 67 12 8. Grit and decomposed porphyry with pinkish gray, sub angular and rounded Section V (No 5 of Section sheet). Altitude of surface is 1103 feet A. T. 1. Clay.... 2. Limestone, light gray, strongly effervescent, little or no quartz 3. Sandstone, calcareous very fine-grained.. .... 29 164 .... 291 5. Grit and decomposed porphyry ("wash"), brick-red, grains of quartz and limestone, effervescent. .... 6. Decomposed porphyry. Total thickness... Section VI (No. 6 of Section sheet). RECORD OF IRON MOUNTAIN DRILL-HOLE. FT. 1. Clay.... 20 2. "Clay rock," light yellow, strongly effervescent, arenaceous 5 3. Limestone, dull gray, fine-grained, arenaceous, effervescent. 4. Limestone, gray, somewhat arenaceous, effervescent, fine-grained.. 14 5. Limestone, white or light gray, coarse-grained, crystalline, dolomitic, little or no quartz..... 16 6. Grit and decomposed porphyry, brick-red, calcareous, with quartz. 2. Limestone, yellowish gray, strongly effervescent, silica in very fine particles 3. Opening ("cave") FT. 18 4. Limestone, reddish-gray, strongly effervescent, gritty and ferruginous... 5. Porphyry ("wash"), decomposed, brick-red, strongly effervescent. 6. Porphyry, decomposed.. 7. Porphyry, hard, light brown, somewhat effervescent. Total thickness Section VIII (No 8 of Section sheet). RECORD OF IRON MOUNTAIN DRILL-HOLE NO. 22. FT. 1. Clay.. 17 2. Sandstone, light yellow, coarse-grained, non-calcareous or very slightly so........ 3. Sandstone, pale yellowish-gray, finer grained, grains round to sub-angular, noncalcareous. .... 45 228 4. Limestone, gray, fine-grained, slightly effervescent, arenaceous... 5. Limestone, light drab or gray, very feebly effervescent, a good deal of quartz in very fine particles; more of a fine siliceous shale than a limestone. 6. Porphyry ("wash"), decomposed, pink, effervescent, arenaceous Total thickness..... 1. Clay... Section IX (No. 9 of Section sheet). 2. Limestone, yellow, gray and pink, effervescent, little or no quartz. 3. Sandstone, fine-grained, pinkish and gray, effervescent 4. Sandstone, gritty, coarse, quartz grains somewhat angular, effervescent 5. Sandstone, finer grained, gray, very slightly calcareous... FT. 12 28 70 39 29 6. Sandstone and grit of quartz grains and porphyry fragments, non-calcareous... 46 7. Sandstone, gritty, decomposed porphyry and quartz, strongly calcareous........ 13 8. Porphyry, decomposed, with pinkish clay, porphyry fragments and quartz, iron ore in lower part, highly calcareous.. 2. Sandstone, pinkish-yellow, sub-angular quartz particles of medium size, cemented in part with iron oxide; some grains of porphyry; slightly calcareous......... Limestone, gray, magnesian, but strongly efferescent; large amount of quartz present.... 3. 4. Sandstone and limestone; samples at various depths are as follows: At 126 ft., sandstone, finer grained than (2), pinkish, strongly calcareous. 173 ft., limestone and sand, gray, with quartz; powder effervescent. 81 20 115 |