322 SECTIONAL TRANSACTIONS.— C. 



and this is associated with the production of a hummocky area. Pressure was greatest 

 in the centre of the area. 



This structure is a clear example of glacial tectonics. -Lenticles of englacial 

 material became incorporated in ice during its southerly passage over Cretaceous 

 strata, and this material, embracing sandstone, &c, must have been derived from out- 

 crops in the vicinity, the plane of ' gumbo ' clay to the north forming a suitable floor 

 for ice movement. The repetition of similar lithological material by thrust produces 

 imbricate or ' schuppenstruktur.' Material between two neighbouring thrust planes 

 may be regarded as being moved en masse. The contortions include (a) compression 

 folds due to lateral pressure, and (6) flow curves of subsequent deformation by pressure. 

 They display drag phenomena. The association of thin plastic clays with sand offered 

 a most favourable material for incorporation as englacial material in a moving body 

 of ice. The structure represents the final stages of the deglaciation of the area and 

 belongs to the stagnant glacier type of glacial tectonics. 



The cost of this investigation was defrayed by a grant from the Sladen Trustees, 

 1924, for which I express my thanks. 



Mr. Herbert P. Lewis. — The Zoning of the Avonian Rocks in the South of 

 the Isle of Man. 



The lower beds (Lower Limestone of Cumming), as developed above the Basal 

 Carboniferous Conglomerate from Cass-ny-Hawin to the east side of Castletown Bay, 

 at Port St. Mary, at Ballasalla and at Ballohot, find their closest parallel in the 

 Michelinia and Productus corrugato-hemisphericus zones of the N.W. Province as 

 defined by Prof. Garwood. 



In the Michelinia zone, which in places is oolitic, the lowest persistent fossil band 

 is rich in Syringothyris cuspidata var. exoleta and contains Athyris glabistria, 

 Cyathophyllum mullilamellatum, &c. Higher in these C 2 beds the C'honetes carinata 

 band with Michelinia grandis, ClisiophyUummultiseptatum, &c, has been traced from 

 Cass-ny-Hawin to the east side of Castletown Bay. The highest Michelinia beds at 

 Ronaldsway contain Punctospirifer glabricosta, Zaphrentis cf. ennislcilleni, and bryozoa. 

 These and associated fossils occur near the base of the limestone and above beds 

 with Syringothyris at Port St. Mary. The same band is found at Ballasalla and 

 Ballohot. At Port St. Mary and Ballasalla, immediately above this band, are beds 

 containing mollusca (' gasteropod beds') which indicate a low horizon in S,. At 

 Ballohot the presence of Nemalophyllum minus, Chonetes papillionacea, &c, indicates 

 the top of S 2 . In the intervening S beds P. corrugato-hemisphericus is found, but 

 fossils are not common. 



In the coast-section at Strandhall Nemalophyllum cf. minus occurs below T>i beds 

 which yield Cyathophyllum murchisoni; a higher band with Chonetes cf. comoides is 

 probably near the top of Dj. Beds near the top of this section contain Zaphrentis 

 costaia and show analogy to the Cyathaxonia beds of Scarlet which are near the top of 

 D v The Scarlet-Castletown beds with Prolecanites compressus (Merocanites) pass up 

 into beds with a knoll fauna at Knockrushen. 



The knoll limestone (Poolvash Limestone of Cumming) is divisible into two zones: 

 a lower with Beyrichoceras micronotum and B. vesiculifer, and an upper with Ooniatites 

 crenistria and Beyrichoceratoides truncatum. Near the base of the higher zone is a 

 coral band with Dibunophyllum cf. muirheadi, &c. 



The black limestone (Posidonomya Schist of Cumming) yields Prolecanites serpen- 

 tinus, Ooniatites punctatus, and O. falcatus near the base, below the interstratified 

 ' breccia bed ' of knolly limestone which contains Cyathaxonia, Emmonsia parasitica, 

 and small Michelinias. Above the ' breccia bed ' the black limestone fossils include 

 Posidonomya becheri, O. falcatus, and goniatites of the C. striatus gens. These lower 

 P x beds of Bisat are the highest beds exposed. The Poolvash beds are comparable 

 with those of Cracoe. 



Wheelton Hind's view that none of the limestone was deposited before D. 2 time is 

 therefore considered untenable, as there is evidence of continuous deposition from C 2 

 until Lower Bowland Shale time. Cutting out of the lower beds between the 

 Punctospirifer band and the basal conglomerate at Port St. Mary indicates westward 

 transgression of the C. i — S : sea on to a pre-Carboniferous ridge of land which, it is 

 thought, never became wholly submerged in Lower Carboniferous times. 



