94 



MOUNTAIN LIMESTONE, DERBYSHIRE. 



1. The first limestone 150 feet, with much white chert. 



2. The first toadstone 48 feet, vesicular and amygdaloidal. 



3. The second limestone 150 feet, contains beds of magnesian 



limestone. 



4. The second toadstone 128 feet, more compact than the first 



loadstone. 



5. The third limestone 180 feet, contains black madrepore beds. 



6. The third toadstone 66 feet, uncertain. 



7. The fourth limestone not pierced through, uncertain. 



This may be an approximation to the thickness of the five upper 

 beds near Matlock Bath, but is by no means an accurate statement of 

 the succession and thickness of the beds in other parts of the coun- 

 ty. It may be proper to remark also, that 'the limestone is distinctly 

 stratified, and the strata of limestone are often divided by strata of 

 clay, provincially called way-hoards, and also by strata or rather 

 seams of siliceous stone called chert, resembling flint, but less splin- 

 tery in the fracture, and fusible ; which latter property is doubtless 

 owing to an admixture of calcareous earth. These strata of chert 

 occur most frequently in the upper limestones ; they contain, like the 

 limestones, remains of shells and encrinites. As loose blocks of 

 chert with encrinites are sometimes ploughed up in the fields, Mr, 

 Farey supposed that these blocks have been converted from lime- 

 stone into chert by some unknown process, — an opinion for which 

 there is not the slightest foundation. The chert blocks are the re- 

 mains of hard strata, which have resisted decomposition or destruc- 

 tion, in the same manner as nodules of flint in the upper chalk. 

 Large bivalve shells (Productus) are found both in the limestone and 

 chert. The thick beds of toadstone that divide the upper from the 

 lower limestones, were supposed by Mr. Whitehurst to have been 

 protruded between them in a state of fusion : this opinion will be 

 examined subsequently. Admitting its truth, it would sufficiently 

 account for the great irregularity in the thickness and succession of 

 these beds, which is known to prevail throughout the Peak of Der- 

 byshire. All the miners that I have examined on the subject, agree 

 that the warm springs which abound in the vicinity of Matlock, rise 

 from under the second toadstone, and that when this bed is first pier- 

 ced through, the water has often a higher temperature than the Mat- 

 lock Bath water, but its heat is reduced by admixture with cool 

 springs in the upper beds. 



I have now to observe that the descending series of limestone and 

 toadstone to No. 5., or the third limestone, may all be found in the 

 vicinity of Matlock, and many other parts of the mining district ; 

 but the beds of toadstone are of variable and uncertain thickness. 

 With respect to the third toadstone, its occurrence as a regular bed 

 is extremely doubtful. In some situations there are eruptions of 

 toadstone intervening in the third limestone, which is of vast thick- 

 ness, but these beds of toadstone are in general extremely irregular : 



