228 Review of ^^ Outlines of thi 



are annually raised in these counties out of this formation. 

 Now a ton of coal is very nearly one cubic yard ; so that 

 the yearly loss from mining amounts to 2. 8 millions, or 

 (adding a third for waste) to 3. 7 millions of yards. Accor- 

 ding to this statement, the Newcastle coals may be mined 

 to the present extent for 1500 years before they be ex- 

 hausted. But from this number we must deduct the amount 

 of the years during which they have been already wrought. 

 We need not be afraid then, of any sudden injury to Great 

 Britain from the exhaustion of the coal mines. It is neces- 

 sary <o keep in mind, likewise, that I have taken the great- 

 est thickness of the coal beds. Now as this thickness is 

 far from uniform, a considerable deduction (I should con- 

 ceive one third of the whole) must be made in order to 

 obtain the medium thickness ; so that we maj' state in 

 round numbers that this formation, at the present rate of 

 waste, will supply coal for 1000 years, but its price will be 

 continually on the increase, on account of the continually 

 increasing expense of mining." It appears that in the 

 above estimate of Dr. Thomson all the beds of coal are 

 calculated upon as co-extensive throughout the whole field ; 

 whereas allowance ought to have been made for the small- 

 er extent of the upper beds which first crop out. It is also 

 probable that the consumption of coal now materially ex- 

 ceeds that taken into the account: for both these reasons 

 we must deduct a century or two from the calculation." 

 p. 371—372. 



It is unnecessary to refer to the numerous coal forma- 

 tions in this country. We merely remark, that a minute 

 and scientitic description of these is a desideratum in our 

 geology ; and it is high time, also, that we should make a 

 distinction between the anthracite* and bituminous coal 

 formations, since they are obviously referable to different 

 epochs. 



Mill Stone Grit and Shale. These rocks lie immediately 

 beneath the coal measures and alternate with each other. 

 The shale does not materially differ from the slate-clay of 

 the coal formation ; and the mill-stone grit is a coarse 

 sandstone, consisting of quartzose particles of various sizes, 



* That elliptical transition formation, (embracing the Rhode Island an- 

 thracite) extending' from Boston to Newport, appears to us from a slight 

 examination, to be very interesting and instructive : and since there is an 

 University near each focus of this ellipse, may we not expect, that erelong, 

 we shall be presented with a complete elucidation of iti" 



