Geology of the Neighbourhood of Weymouth, S^c. 23 



meridg-e clay, which is now covered up with sand, and which at that time 

 presented the appearance of slate burnt to the condition of red tiles ; we 

 have now strong reason to presume that such combustion may have taken 

 place, since we have at this moment before our eyes the pseudovolcanic phe- 

 nomena that are exhibiting themselves in the same stratum of Kimmeridge 

 clay near the east extremity of Ringstead Bay, at Holworth Cliff, adjacent to 

 the promontory of White Nore. This pseudovolcanic combustion began in 

 September 1826, and during a period of many months emitted considerable 

 volumes of flame, probably originating in the heat produced by the decompo- 

 sition of the iron pyrites with which this shale occasionally abounds ; in the 

 same manner as in the year 1755, a spontaneous combustion arose and con- 

 tinued during several years in the bituminous shale-beds of the lias in the 

 cliffs at Charmouth ; — we have a description of this circumstance in the Che- 

 mical Essays of Bishop Watson : it is probable that in each case rain-water 

 acting on iron pyrites has set fire to the bituminous shale ; thus ignited, it has 

 gone on burning at Holworth unto the present hour, and may still continue 

 smouldering for a long series of years, the bitumen being here so abundant 

 in some strata of the shale, that it is burnt as fuel in the adjoining cottages ; 

 the same bituminous shale is used as fuel in the village of Kimmeridge, and 

 is there called Kimmeridge coal. 



This pseudovolcano at Holworth commenced in the face of the cliffs about 

 twenty feet above the sea ; its combustion was proceeding feebly when we 

 saw it in September 1829, and it emitted no flame ; there was no appearance 

 of any crater, nor has there ever been any kind of explosion. The extent of 

 the surface of clay which has been burnt does not exceed fifty feet square. 

 Within this space are many small fumaroles that exhale bituminous and sul- 

 phureous vapours, and some of which are lined with a thin sublimation of 

 sulphur ; much of the shale near the central parts has undergone a perfect 

 fusion, and is converted to a cellular slag. In the parts adjacent to this 

 ignited portion of the cliff", where the effect of fire has been less intense, the 

 shale is simply baked and reduced to the condition of red tiles, like that on 

 the shore near Portland Ferry. Should a similar ignition ever take place in 

 the cliffs at Kimmeridge, which are so much more abundantly impregnated 

 with bitumen, the fire may be propagated there for centuries, until the whole 

 of the bitumen is consumed. 



Coralline or Oxford Oolite, and Calcareous Grit. 



The general thickness of this formation near Weymouth is about 150 feet. 

 It contains beds of oolitic limestone resembling the oolite of Heddington, 



