1892.] NATURAL SCIENCES OF PHILADELPHIA. 83 



where large portions, sometimes amounting to more than two-thirds 

 of the original beds, have been carried bodily away along with their 

 adjacent protecting rocks, the detritus now resting far out on the 

 sea bottom, or scattered along the ancient channels of drainage 

 long since obsolete and covered deep with foreign material. 



Again, much of the coal which has escaped this ruin possesses 

 little or no present or future economic value because of such reasons 

 as the following : 



1. Its crushed and impaired condition, due to repeated and ex- 

 cessive flexures, overturuings and fractures. 



2. Its detached position in small separate residuary basins 

 caused by erosion and entire loss of the adjacent anticlinals, thus 

 forbidding the permanent aj^plication of the large amount of 

 capital required to exhaust such small separate areas. 



3. The thinness of many of the beds, which do not, and never 

 can admit of mining by any process of extraction, without removing 

 more rock than coal. 



Nothing need be said of mere depth, since the article being one 

 of prime necessity, as it becomes scarcer it will be mined at all 

 depths, the increased cost being compensated by advanced price. 

 In England there is no doubt that if the "South Eastern bed" 

 shall be satisfactorily verified, it will be immediately mined though 

 its most ardent advocates give it a minimum depth of 3000 feet. 



Nevertheless it is evident that large deductions must be made 

 from the area of the carboniferous measures as these are known to 

 geologists and adopted in the Census reports, before even an 

 approximate knowledge can be reached of the extent of actual coal 

 beds, adapted, as respects separate area and thickness, to supply 

 remunerative coal at this or any future period. How large such 

 deductions should be, we possess at present insufficient data for 

 computing with accuracy, but from the general observations now 

 possible to make, and from the Avell known tendency of many 

 property owners to exaggerate the resources and value of their pos- 

 sessions whether in reports to Census officials or miscellaneous 

 observers, we may be sure they must be sufficiently large to effect a 

 very material reduction of the general area of the measures, before 

 arriving at the actual area of mineable coal. 



It would therefore seem quite a liberal estimate if such reductions 

 were offset against the following items not included in the Census 

 report, viz : 



