MORRIS BRITISH FOSSILS. 



139 



Upper Silurian. 

 (Thickness, 5,000 feet.) 



Tilcstone and Ludlow beds. 

 Wenlock and Woolhope beds. 



MiDDM Silurian. Lower Silurian. 



(Thickness, 2,000 feet.) (Thickness, 19,000 feet.) 



Caradocand Bala. 



Upper and lower 

 Llandovery rocks. 



Llandeilo flags 

 Lin^^ula beds. 



LoNGMYND or BoTTOM RocKs, or Lower Cambrian of Sedgwick. (Thickness, 



26,000 feet.) 



A. Lower Cambrian (Sedgwick). 



Lower Cambrian, Sedgwick, Lyell ; Cambrian, Longmynd, or Bottom rocks, 

 Murchison, and the Geological Survey ; Cambrian, in part, rhillips ; Tremadocian, 

 in part, Woodward ; Huronian, Lor/an. 



Harlech grits, Bangor & 

 Llanberris slates, 

 Longmynd schists, 

 St. David's schists ; 

 in Wales. 



Skiddaw slates 

 and grit-stones, 

 Cumbria. 



(Lower Cumbrian 

 of Sedgwick.) 



Ross-shire con- 

 glomerates, 

 Scotland. 



Grits and slates 

 of Wicklow and 

 Wexford, Ire- 

 land. 



The lower Cambrian rocks of Wales consist of grits and conglo- 

 merates, at Harlech, and of alternations of gritstones and slates at 

 Eangor and Llanberris; the latter place affording the best roofing- 

 slates. The probable equivalents of these rocks in Anglesea are con- 

 torted and crystalline schists, of gneissose, micaceous, and chloritic 

 characters. The Longmynd and Haughmond hills of Shropshire 

 consist of a thick series of dark purple and greenish schists, grits, and 

 sandstones, estimated at 26,000 feet in thickness. These flagstones 

 exhibit trails and holes of worm-like animals, also ripple-marks, and 

 other evidences of littoral or shallow-water conditions. They also yield 

 relics of a trilobite. Similar rocks, but apparently without fossils, 

 occur near St. David's, in South Wales. 



To this division Professor Sedgwick refers the Skiddaw slates and 

 grits of Cumberland ; these are of great thickness. The purple and 

 green grits and slaty rocks, with occasional interstratified quartz, of 

 Bray Head, Wicklow, and the adjacent coast, in Ireland, belong to this 

 group. In their upper portion have been detected numerous worm-like 

 markings, and the curious fossil known as Oldhamia. 



The great red conglomerates and sandstone of the north-west of 

 Sutherland and Ross, in Scotland, have lately been proved to be of this 

 lower Cambrian age. 



The fossils of these rocks are very few, comprising doubtful remains 

 of fucoids, traces of sea- worms, and a branched zoophytic form, pro- 

 visionally referred to the JBrjozoa. * 



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