544 Aubrey Strahan — Rocks beneath the Coal-measures 



quartz and other rocks. This grit rests on the greenish and purplish 

 coarse conglomerate or breccia mentioned above. A better exposure 

 of the lower beds is found in the entrance to a quarry half a mile 

 south-east of Hartshill. There there occur in the quartzite thin 

 bands of intrusive igneous rocks much decomposed. The lower beds 

 of the quartzite consist of bands of conglomeratic grit, well bedded 

 and split up with shaly partings, and strongly impregnated with 

 manganese. The conglomerate is seen for a thickness of more than 

 eight feet, but the actual base is not exposed. There are also a few 

 conglomeratic bands higher up in the quartzite, with pebbles ranging 

 up to half an inch in diameter. 



I may remark here that the Blue Hole and both the sections in 

 which the basement conglomerate is exposed have been opened since 

 the original survey of this district was made, and that it was there- 

 fore almost impossible at that time to determine the nature of the 

 rock beneath the quartzite, and its relation to this formation. The 

 true nature of the (Jaldecote Series and of the basement conglomerate 

 of the quartzite was first detected by Prof. Lapworth. 



The great mass of quartzite overlying this basement conglome- 

 rate is an intensely hard fine-grained siliceous rock, in which the 

 original sand-grains are so closely cemented together by silica as to 

 have almost lost individuality. The rock, however, is well bedded, 

 and contains thin bands of green or purplish shales. It is used most 

 extensively for road-metal, and nearly the whole series of beds is 

 exposed in one or other of the great quarries. The quartzite is also 

 traversed by sheets of intrusive igneous rocks, ranging from. 3 to 

 over 100 feet in thickness, and following the bedding with remark- 

 able regularity. The igneous rocks are usually quite decomposed to a 

 depth of from 30 to 40 feet from the surface, especially when in thin 

 beds. They are locally known among the quarry men as "Dun Dick," 

 and when sufficiently fresh are " cut " (broken to size) into paving 

 cubes. The price of the quartzite road-metal is 3s. a ton when 

 broken to size. I was informed that a prepared cubic inch of quart- 

 zite crushed at a pressure of 24,000 lbs. to the square inch, the 

 igneous rocks yielding at between 11,000 and 12,000 lbs. to the 

 square inch. 



A good exposure of one of these intrusive sheets is found in the 

 Midland Company's Quarry at Nuneaton Midland Station. The 

 quarry is principally in this thick sheet, the eastern part only being 

 in quartzite. The jointing of the igneous rock, which at a distance 

 resembles bedding, is nearly at right angles to the bedding of the 

 quartzite, that is, perpendicular to the plane along which the melted 

 rock has been injected. In this quarry the basement-bed of the New 

 Ked Sandstone may be seen lying across the edges of the quartzite 

 and igneous rock, as will be described subsequently. Another great 

 sheet is seen in the cutting by which a quarry on the east side 

 of the high road, one-third of a mile south of Caldecote Windmill, 

 is entered, and again close to the windmill. This sheet forms the 

 boundary up to which the old quarries along the road were worked. 

 Most of the quarries now worked are in beds below this sheet. 



