290 



Professor E. J. Garwood- 



The Vivi'parus Shale. — Tkis bed, which rested on the surface of the 

 Silurian rocks, consists of a friable sandy mudstone, devoid of any 

 appreciable calcareous constituents ; it averaged about 2 inches 

 in thickness, and was traversed by numerous irregular cracks. 

 The fossils occur exclusively in the highest layer of the deposit.. 

 The majority of the forms are gastropods, evidently belonging to 

 a species of Viviparus, but associated with these, occur numerous 

 examples of a thin-shelled lamellibranch. The bed itself is totally 

 different, not only from the Lamellibranch Limestone which overlies 

 it, but from any other deposit hitherto met with in the lower 

 Carboniferous rocks in the north of England. It has all the 

 appearance of a sandy mud laid down in a freshwater pond 

 on land. Under the microscope the deposit is seen to be composed of 

 closely set alternating layers of coarse and fine material consistmg 

 of abundant sub-angular fragments of quartz embedded in a brown 

 impalpable mud ; a notable quantity of iron pyrites is also present, 

 which frequently occurs in thin layers lying parallel to the bedding 

 planes. 



Fig. 1. — Diagram section of the base of the Carboniferous exposed in 1889, 

 200 yards N. of Gillet Brae. Si, Silurian ; V, Viviparus shale ; 

 L, Lamellibranch limestone ; CC, Cyrtina carhonaria shale ; NM, 

 NematopJiyllum viinus limestone. 



The character of the jointing resembles shrinkage cracks due to 

 desiccation rather than to movements like those to which the dip 

 and strike joints which traverse the overlying massive limestone 

 are probably due. The pond cannot have been of any great 

 dimensions as the deposit does not extend back into the present 

 floor of the quarry, where the crushed Cyrtina Shale lies directly 

 on the Silurian floor. It is also absent from the face of the escarjD- 

 ment to the north and south where the main 'mass of the lime- 

 stone with NematopJiyllum minus overlaps on to the Silurian.. 

 Again, the shaly lim.estone which overlies the conglomerate in 

 Gillet Brae, 200 yards to the south, contains no trace of this deposit. 

 The pond may, however, have extended to the east, but again no 

 trace of it has been found on the east side of the Kibble valley, 

 where the base of the Carboniferous is exposed near Douk Gill and 

 to the north of Dub Cote. 



