88 SINGULAR CONTORTIONS OF TRANSITION LIMESTONE. 



negated, veined, and spotted. It may be stated generally, that tran 

 sition limestones are seldom so perfectly crystalline as primary lime- 

 stones, and they have rarely the compact and earthy texture of se- 

 condary limestones. 



Transition limestone occurs in beds alternating with slate, grey- 

 wacke, greywacke-slate, and coarse gritstone. Some of these beds 

 are of considerable thickness, and form mountain masses. The 

 lowest beds alternate with slate ; they contain few organic remains. 

 The variegated limestone of Devonshire is of this kind. Sometimes 

 numerous thin strata of slate and transition limestone alternate, and 

 are much bent and contorted. A very remarkable instance of this 

 occurs at Drewsteignton, near Moreton, in Devonshire, where a se- 

 ries of thin strata of dark Hmestone alternate with strata of indurated 

 slate, and are bent and folded in various directions. Were we to 

 take a number of alternating sheets of black and brown paper, and 

 fold them nearly round a wine decanter, and then bend them back 

 over the lower folds, we should have a not unapt representation of 

 the singular contortions of the strata in this place, where they are ex- 

 posed to view by extensive quarries cut in the rock. 



The remarkable contortions of the beds of transition limestone and 

 slate, imply the operation of a cause that could not only bend but 

 soften the strata ; and were we to admit that granite has once been 

 in a state of fusion, and been protruded through the outer crust of 

 the globe, the immediate contiguity of these bended strata to the 

 granite of Dartmoor, might indicate the agent by which the effects 

 were produced. Near Dudley, in Staffordshire, we have another 

 remarkable instance of the bending of beds of transition limestone ; 

 but this is in the vicinity of basaltic rocks, which are now admitted 

 to be of igneous origin. 



The limestone at Wren's Nest, near Dudley, consists of two beds 

 — one ten, and the other fourteen yards thick, resting upon beds of 

 soft and imperfect limestone and shale, called wild measures. The 

 two beds of limestone are separated by similar strata of wild meas- 

 ures, thirty-eight yards in thickness ; they are raised up together in a 

 position approaching to vertical, are folded round the hill, and en- 

 close a space of about fifty acres, with a double wall of limestone 

 rising above the country, like an oval tower widening at the lower 

 part. 



If two sheets of pasteboard were separated by a quire of blue pa- 

 per and laid flat, and a blunt metallic rod were thrust through the 

 whole from beneath, it would force the lower sheet of pasteboard 

 through the upper sheets, and represent the present position of the 

 strata at Wren's Nest Hill. At Dudley Castle Hill, about a mile dis- 

 tant, the beds of limestone are bent, and dip on each side of the 

 hill. (See a section of this hill, Plate III. fig. 4.) 



A, Wren's Nest Hill ; a a, b b, the two beds of limestone enfold 

 the hill, as represented in the small compartment e, above the sec« 



