Vol. 51.] OF THE MID-COTTESWOLDS. 389 



Introduction. 



This essay is partly supplementary to my previous communication 

 to the Society on the ' Bajocian of the Sherborne District,' l which 

 will be alluded to as my former paper ; but in the main it is entirely 

 distinct therefrom. I divide it into three parts : — Part I. dealing with 

 the district from Stroud to Leckhampton, and showing, among other 

 matters, the relative extension of the Gryphite- and Lower Trigonia- 

 grits ; Part II. noting the discovery of an ammonitiferous horizon r 

 thus making an addition to the Bajocian of the Cocteswolds; and Part 

 III. giving the faunal sequence of brachiopoda in the Cotteswolds 

 and in Dorset, so as to aid in the local correlation of strata in the 

 former, or any other district where ammonites may be absent. 



Definitions of Terms. 



The following terms, which it will be necessary to use in this 

 paper, require explanation : — 



Bajocian. — In a postscript to my former paper (p. 521) it was 

 suggested that the Bajocian might be used as ' a chronological 

 term to coincide with the acme and paracme of the Sonniniuae,' and 

 ' it would comprise the hemerae discitce, Witcliellice, Sauzei, and 

 Humjihriesiani.' It is used in this sense in the present paper, 

 though, as will be shown in subsequent pages, no strata deposited 

 during some of these hemerae are found in the district reviewed. 



Mid-Cotteswolds. — In his work on the Cotteswold Hills, Lycett 

 divided the Cotteswolds into Southern and Northern, taking the 

 Yale of Stonehouse (the valley of the Frome) as the dividing-line 

 (p. 7). In other cases, however, the term ' Northern Cotteswolds ' 

 seems to have been applied to the district north of the Chelt, and 

 the term has perhaps been used somewhat loosely. For geological 

 purposes it seems convenient to divide the Cotteswolds into three 

 portions, and to define these districts with some precision. The 

 following arrangement is, therefore, proposed : — That the Cottes- 

 wolds be divided into Southern, Middle, and Northern, as these 

 divisions will be found characterized by a fair coincidence of geolo- 

 gical and geographical features — the Southern Cotteswolds to extend 

 from the valley of the Avon (Bath) to the valley of the Frome (Vale 

 of Stonehouse), a district characterized by the presence of an ammo- 

 nitiferous cephalopod-bed deposited during the hemerae opalini- 

 striatuli. 2 It is also distinguished by an almost complete absence 

 of the ' intervening beds ' (see p. 390), which extend very little 

 south of the Frome Valley. Eastwards, away from the escarpment, 

 the line between the Southern and Middle Cotteswolds might follow 

 the road from Chalford to Siddington (Cirencester), and then, if 

 desired, be extended along the outcrop of the Cornbrash. 



Between the Mid-Cotteswolds and the Northern Cotteswolds the 



1 Quart. Journ. Geol. Soc. vol. xlix. (1893) pp. 479-521. 



2 These auimouitiferous beds extend very little north of the Frome Valley, 

 and then some henierse are not represented by any deposit. 



