Br. T. F. Sihly—The Forest of Dean Coalfield. 419 



palaeontological characters, they present the usual abundance of 

 ostracods and occurrence of modioiiform lamellibranchs ; but their 

 most striking feature is the abundance of Serpula-lWe annelids, or 

 Miteheldeanm-like algse, or both these fossils, in certain bands of 

 calcite-mudstone. The Serpulce often occur in the form of large, 

 fasciculate masses of tubes, but exhibit a variety of forms. 



Main Limestone. This is composed in bulk of dolomites and 

 dolomitic limestones, with a local and variable development, in the 

 upper part, of crinoidal or oolitic limestones vs^hich have escaped 

 dolomitization. 



The lower, and major, portion belongs to the Zaphrentis-zone, and 

 consists for the most part of finely crystalline dolomites, red, yellow, 

 or grey in colour. Fossils are so scarce in these beds that the sub- 

 zones Z-^ and Z2 have not yet been distinguished. 



The upper part is of Syringothyris age (C), and belongs mainly, 

 at least, to the sub-zone Ci. Essentially, this upper portion of the 

 Main Limestone consists of a series of crinoidal limestones capped by 

 a few beds of coarsely crystalline dolomite. The crystalline dolomites, 

 which immediately underlie the Whitehead Limestone, are persistent, 

 and the lower beds of the crinoidal limestone-series are always 

 dolomitic ; but the intervening beds vary considerably in character, 

 both from bed to bed in vertical sequence, and also when traced 

 laterally. The variations in these intervening beds are chiefly 

 due to {a) the very variable extent to which dolomitization has 

 affected the rocks, and {b) the sporadic development of oolitic 

 structure. In some localities all the beds are more or less strongly 

 dolomitized. Elsewhere the dolomitization is distributed irregularly, 

 so that beds of large collective thickness have locally escaped 

 dolomitization. Important deposits of haematite occur in this series 

 of limestones; and the maximum amount of dolomitization of the 

 rocks is found in those localities where the haematite-deposits are 

 well developed. On the evidence collected up to the present, it 

 appears that in this whole series of crinoidal limestones a certain 

 amount of ' contemporaneous ' dolomitization, almost confined to the 

 lower beds, has been followed by extensive but irregularly distributed 

 ' vein-dolomitization ' connected with the formation of the haematite- 

 deposits. 



Whitehead Limestone. This small subdivision is of special interest 

 and importance, inasmuch as it constitutes a well-marked Modiola- 

 phase. The rocks composing it are chiefly limestones, with subordinate 

 calcareous clays which often contain numerous limestone-nodules. 

 Locally, some of the beds are dolomitized. The limestones ai'e very 

 variable in character, but among them finely oolitic rocks and calcite- 

 mudstones of chinastone type predominate. Mitcheldeania--n.o&.u\es 

 and (?) Girvanella--iio(\.\x\&?, are common in many of the limestones, 

 and sometimes so abundant as to form the bulk of the rock. A certain 

 amount of fine quartz-sand occurs in all the beds ; and the occasional 

 intercalation of bands of calcareous grit foreshadows the oncoming 

 of the Drybrook Sandstone, into which formation the Whitehead 

 Limestone passes up conformably. 



I have discovered no fossil evidence to support Dr. Vaughan's 



