234 Dr Hibbert on the Limestone of Burdiehouse 



SECTION I.— THE FRACTURED STATE OF THE STRATA IN THE VICINITY 

 OF THE LIMESTONE OF BURDIEHOUSE. 



The strata with which the limestone of Burdiehouse are more or 

 less connected form the great Mid-Lothian coal-district, of which 

 the neighbourhood of Dalkeith may be considered as the centre. 



Mr De la Beche, in his excellent little system of theoretical 

 Geology, has remarked of the Earth's crust, that there is scarcely 

 an area of eight or ten miles which has not been more or less 

 fractured ; which remark cannot be better illustrated than in the 

 Scottish coal-fields, which may be considered as exhibiting a con- 

 geries of fractured areas, separated from each other by long lines 

 of fissure. 



The rationale of this fractured state is now beginning to be 

 understood, for which we are indebted to an eminent geologist, 

 M. de Beaumont. 



The theory hinges upon the following circumstances : — The 

 interior of our globe has had its temperature diminished sensibly 

 by the reduction of heat, and it has consequently contracted. 

 The earth's crust, however, has preserved, at the same time, a 

 nearly rigorous constancy of temperature, its refrigeration having 

 been almost insensible, and hence little contraction has ensued. 

 Keeping, then, in view these inequalities of contraction, it would 

 follow that, as the interior of the globe must, in length of time, 

 have had its temperature lowered far more than its exterior crust, 

 its capacity must have undergone a proportional excess of dimi- 

 nution. In this case, the external solid crust, in striving to con- 

 form itself to the fluid or viscid surface beneath, and to embrace 

 it more closely, would undergo considerable dislocations ; — and, 

 from a cause so generally operating, fractures would be induced, 

 which would have a greater or less tendency to a parallel direc- 

 tion. 



In the Mid-Lothian coal district decided lines of fracture from 

 these causes must have very early taken place. They have, for 



