364 PROCEEDINGS OP THE ACADEMY OP 



nearly vertical, but they occasionally clip 5, 7, 8 to the west, 

 causing a local inversion. 



The Lyden coal mine lies in an oblong ridge, isolated mostly in 

 a small basin of erosion one mile north of Ralston Creek. 



The ridge, with its weather-worn castellated summit, is 700 or 

 800 feet wide, and nearly one-half mile long ; a parallel outcrop of 

 cretaceous sandstone, dipping east about 30% and succeeded by 

 a ridge of red sandstone, is found one mile west of the coal out- 

 crop. In order then to reach the coal bed in the cheapest and 

 most expeditious manner, a drift was started from the west 

 slope, and, cutting at right angles to the stratification, reached 

 a distance eastwards of 310 feet horizontal, and over 200 feet 

 below the top edge of the sandstone outcrop. At about 270 feet 

 from the entrance of the drift a small vein of coal was pierced 

 through, about 15", then two more larger beds, making altogether 

 about five feet of good coal in three beds. Penetrating east some 

 ten feet beyond the last coal bed, the miners were astonished to 

 find, in place of the ten to twelve feet coal bed, the object of their 

 search, an exceedingly hard black vein of mineral matter, contain- 

 ing geodes of brilliant quartz crystals, and small veins of pyrites, 

 the honeycombed mineral full of a green ochrey powder, with veins 

 of chalcedony, and small orange-colored crystals and concretions. 



Upon further examination I found that this mineral vein, re- 

 sembling a very dark hard iron ore, had apparently been thrust 

 up from below as a "dike," that it had taken the place of and 

 destroyed the coal bed that it had apparently obliterated ; that 

 the country rock, a soft sandstone with clay shale or fine clay, 

 was disrupted, fragmentary, and in irregular order, the intruded 

 "dike" having the appearance of being the produce, or at least at 

 one time subjected to heat; yet the adjacent rock is but little if 

 any changed, and in the vein we find everywhere in small particles 

 unconsumed coal, but more particularly in the hone3'combed por- 

 tions of the mineral. 



Altogether, from the peculiar appearance of the intruded " dike," 

 and its violent intercalation in the recent tertiary strata, we find 

 a complete substitution of the coal took place in this part of the 

 coal outcrop, for by digging upwards good coal is found above 

 the "dike," for another drift has been extended nearh' 200 feet 

 or more in a northerly direction on the workable coal bed. But 

 in this drift, after entering on the coal bed from the south end 



