120 G. Edmonds — 



is the " Girvanella " Band, which occurs at the base of the Eough 

 Beds, dark-grey limestones in which " pseudo-breccia " structure is 

 excessively developed. At Yeathouse Girvanella sp. is found 

 encrusting small fragments of corals, crinoid-stems, etc., and shell- 

 debris in a band of limestone, 2 to 3 feet thick, forming the base of 

 the Eough Beds. The underside of this band has long stick-like 

 concretions attached to it and rests on a 3 inch band of coal-like 

 shale with plant-impressions. Below this is a band, 5 to 8 inches, 

 of dark calcite-mudstone containing Spirorhis-like annelids, ostracods 

 and small gasteropods. In thjs band Girvanella sp. appears as 

 unstained, oval, or nearly spherical bodies, 1 inch or more in diameter, 

 whilst in the higher band it is stained with hematite, and is usually 

 smaller and more ellipsoidal. 



The higher band is recognizable wherever the horizon is exposed, 

 but the " calcite-mudstone ", which is very well developed in the 

 north-eastern portion of the area from Yeathouse onward, is absent 

 from the south-western portion, and is represented at Clints by a 

 shale or mudstone. About 20 feet above the base of the Fourth 

 Limestone is a bed, 3 to 6 feet thick, of mottled shale or mudstone 

 which fills up channels in the limestone below (see p. 82). Where 

 the shale is thinnest, and presumably, where the top of the limestone 

 has not been removed, broad sheets of what appears to be algal 

 limestone occur. On an unweathered surface the band has a land- 

 scape-marble-like appearance, dark-grey " tones " of colouring 

 matter alternating with lighter ones in wave-like undulations. 

 It has also the porcellanous appearance of algal limestone. On 

 a weathered surface sections of some of the patches remind one of 

 the thalli of wall-lichens ; they have reddish centres, with light 

 blue-grey intermediate zones, and darker zones towards the incurved 

 edges. In other specimens the organisms stand out from the 

 weathered surface, and the " undulations " persist in scimitar- 

 shaped " wavfes ", smoothly roanded crest alternating with 

 sharply angular dip, in some cases for many feet, the average 

 distance from " crest " to " crest " being half an inch. The 

 organism may be referred with some certainty to the calcareous 

 algae, but has not as yet been identified ; the band is well exposed 

 at intervals throughout the district. The fourth band, which is 

 badly exposed, occurs as a nodular bed between the Sixth and 

 the Seventh Limestone. The nodules appear to be similar to the 

 masses in the highest band. 



Contemporaneous Pot-holes. 



At two or three horizons " pot-holes " or " pitted " limestones 

 occur. The " pot-holes " are of two kinds, the one regular and 

 quasi-cylindrical and the other V-shaped in section. The regular 

 and quasi -cylindrical type occars at the top of a thick post of 

 limestone (20 feet at Clints and 26 feet at Salter Hall), lying 

 immediately below the limestone with abundance of Saccammina 



