Ati^: 26, 1875] 



NATURE 



351 



correlations of the then so-called Transition rocks were not un- 

 derstood ; therefore they help us little toward a correct under- 

 standing of their age and character ; it was not until Murchison 

 had succeeded in making out the true relation and character of 

 the upper fossiliferous beds beneath the Old Red Sandstone, and 

 had arranged his grouj)s by their organic remains in consecutive 

 order under the name of the Silurian System, that the true age 

 and relation of the Transition strata of Tortworth were under- 

 stood. It then appeared that the Silurian rocks of Tortworth 

 are the southern extension of the same formations which, extend- 

 ing through Micklewood Chase and the Vale of Berkeley, appear 

 as a dome of Upper Silurian, rising near Tites Point on the left 

 bank of the Severn near Purton Passage. The same rocks are 

 found wrapping round the base of May Hill and Huntley Hill 

 in the Forest of Dean, in the Valley of Woolhope, Herefordshire, 

 on the western slopes of the Malvern Hills, and extending through 

 Eastnor and Ledbury to Wenlock Edge, Salop. Whatever, 

 thereibre, is true relating to the PaljEontological character of the 

 Upper Silurians in these other localities, is equally correct of the 



same formations that lie m the miniature basin of Toitworth. 

 The Caradoc Sandstone, or, as it is now called, the Upper 

 Llandovery Sandstoue, is the oldest rock at Tortworth, and forms 

 the dominant stratum of the district. It covers an oxtensive 

 area ; and some small sections are seen at the south side of 

 Micklewood Chase, and on both banks of the Avon near Damory 

 Mill. Lithologically and paliEontologically it is indistincrnishable 

 from hand specimens of the same formation at May Hill. It 

 abounds in fossils : Pentanierus, Strophomena, Orthis, Atrypa, 

 Spirifera, and LcpUena, with broken Trilobites belonging to the 

 genera Trimideus, Calymene, L'licnus, and Phacops, aie found, 

 together with the stems of Crinoids and Tentaculites. 



The Wenlock Limestone is exposed at Falfield Mill and Whit- 

 field, and other places ; from its various beds the characteristic 

 Upper Silurian Corals are collected, as Favosites, Syringopora, 

 Halysites, Forites, Caryophyllia, and Acervularia. Crinoidal 



1 stems are very ab«ndant. Many Brachiopoda, as Leptana, 

 Atrypa, Orthis orbicularis, and Gasteropoda, as Euomphalus 



, discors and Euomphalus funatus, are collected, vntb fragment* 



Table I.— Geological Formations in the Bristol Districts. 



Periods. 



Post Tertiary - 



Tertiary - 



CRETACtOUS 



Divisions. 



Jurassic 



LlASSIC 



Triassic - 

 Permian - 



Carhoniflkucs - 



DhVUMAN - 



Upper Silurian 

 Igneous Rucks - 



j Recent - 



1 Post Pliocene 



Upper Oolite' 

 Middle Oolite 



Lower Oolite - 



Upper Lias - 



Middle Lias - 



} Lower Lias - 



I Upper Trias - 



Formations. 



I ! Upper - 

 I , Lower - 



Old Red 



Alluvium . . - 

 Peat .... 

 Gravel - ■ - - 



I Greensand ... 



j Coral Rag 



I Oxford Clay - 



j Combrash 

 Forest Marble 



j Bradford Clay 

 Bath Oolite - 



I Fuller's Earth 



I Inferior Oolite 

 Liassic Sands 

 Upper Lias Clay] - 

 Marlstone . . - 

 Clays . . . - 

 Clays .... 

 Limestones - 



I Avicula coniorta 



j Keuper - - - - 



I Dolomitic Conglomerate 



1 Coal Measures 



i Millstone Grit 



1 Upper Shales 



I Carboniferous Limestone 



Lower Shales 



Sandstones 

 j Conglomerates 



Ludlow 

 1 Wenlock 

 I Upper Llandovery - 



Greenstone . . . 



Basalt .... 



Typical Localities. 



Bristol, Shirehampton. 



Cheddar, Glastonbury. 



Cheddar railway, Keynsham, Saltford. 



Absent. 



Postlebury.] 



Absent. 



Cloford. 



Cloford, Marston Bigot. 



Chickwell, Faulkland. 



Bradford. 



Coombedown Lansdown P. 



North Stoke, Lansdown, Box. 



Dundry, Cotteswold Hills. 



Dundry, Midford, Frocester, 



Dundry, Midford, Frocester. 



laundry, Sodbury, Stinchcombe. 



Dundry, Sodbury, Stinchcombe.' 



Horfield, Pell. 



Keynsham, Saltford. 



Aust, Beechum, Garden ClifT. 



New River, Cotham. 



Bristol, Portishead, Clevedon. 



Absent. 



Mangotsfield, Radstock, &c. 



Brandon Hill, Fish-ponds, &c. 



Clifion, Ashton, Fish-ponds. 



Clifton, Mendips, Tortworth. 



Clifton, Clevedon, Tortworth. 



Clifton, Portishead, Mendips, &c. 



Clifton, Portishead, Mendips, (S;c. 



Berkeley, Purton Passage. 



Tortworth, Falfield. 



Tortworth, Damory. 



Damory, Charfield, Woodford. 



Uphill, Mendips, Weston. 



of Calymene Blumenbachii and Phacops cautlatus. The Ludlmv 

 Koek is best exposed at low-water mark on the west bank of the 

 Severn at Purton Passage, where it rises in a dome-shaped mass, 

 and dips away beneath the beds of Old Red Sandstone of tiie 

 Devonian series on the opposite shore ; the upper portion of 

 tills formation consiats of greenislugrey micaceous beds, with 

 Leptana lata, Orthis unguis, and Terebratula Wilsoui, which 

 piobablv represent tlie Aymestry limestone. 



Devonian. — The Old Red Sandstone, in its upper parts, con- 

 sists of fine-grained thin flagstones of a whitish-grey colour ; and 

 Tortworth Court is built of these fine Ijuilding beds. This 

 upper division is underlain by course quartzose conglomerates, 

 and at the base by red sandstone, which re>>ls on the Llandovery 

 strata. The same succession of beds is very persistent, with 

 conglomerate in the centre and lower third, and sandstone above 

 and at the base. 



Carboniferous. — The Bone Bed at the base of this formation is 



well developed, together with the Lower Limestone Shales. 

 Psammudus Itneatis, P. Uevissimus, Coprolites, and Pileopsis 

 angustus. Phi!., a sliell of the Carboniferous Limestone, are the 

 leading fossils here. 



Millstone G>it and Coal Measures. — These beds have been 

 fully and accurately described in the "Geological Transactions," 

 by Weaver, Buckland, and Conybeare, accompanied l)y many 

 valuable sections. They consist of Millstone Grit, Lower Coal 

 Measures, Pennant Sandstone, and Upper Coal Measures; the 

 whole series may be studied and examined in this district. A 

 section constructed from Tortworth Green to Frampton Cotierell 

 gives tlie following : — Tortworth Green, Old Red ; the Court 

 and Park, Lower Limestone Shales; Ley Hill and Cromhall. 

 Carboniferous Limestone ; Cromhall Heath, Millstone Grit ; 

 Sweethouse, Lower Coal Shales ; Sweethouse to Robin's-wood 

 House, Pennant, and from Robin's-wood House to Frampton 

 Cotterell, Upper Coal Measures of the Coal-pit Heath V.i in 



