Page:VCH Lancaster 1.djvu/65

 GEOLOGY Bolton and Bury Area The chief fault is that known as the Great Irwell Valley Fault, having a downthrow to the east of over 1,000 yards, and crossing the whole of south Lancashire. Further to the south it is con- tinued into the Trias of Cheshire. A great fault bounds the north-east border of the Manchester Coalfield, and passing N.N.W. across the Trias, runs fairly parallel to the Irwell Valley Fault across the coalfield to a little west of Bury. WiGAN AND St. Helen's District The main faults of this district are the Great UphoUand Fault, with a downthrow of 650 yards and a set of five faults at nearly equal distances of 1,400 yards from one another ; these are : — 1 . Great Pemberton Fault. 2. Great Shevington Fault. 3. Giants Hall Fault. 4. Great Standish Fault. 5. Great Haigh Fault. All the faults mentioned thus fiir belong to the N.N.W. or post- Jurassic System. They are accompanied by smaller faults which run out from them at acute angles or remain parallel, and by a system of east and west faults of less importance which break up the ground between them. This latter series was doubtless in part developed when the Pendle range system of folds was formed. COAL MEASURE FLORA The flora of the Lancashire Coal Measures has long been famous, largely because of the excellent preservation of vegetable tissues in nodules overlying the Bullion Seam or Upper Foot Coal. These nodules supplied material to Lindley, Hutton, Brongniart, Binney, Carruthers, Williamson, Solms-Laubach, and Hick, whereby they were enabled to throw a flood of light upon the structure and relationship of the coal flora. The study of the minute structure of coal plants has also been a favourite subject with the miners, and many can be found to-day with valuable cabinets of coal slides and all the machinery necessary for their production. Their knowledge of the structure of these plants is considerable, and Williamson and others have testified repeatedly to the energy and skill with which these men have prosecuted their studies and produced valuable results. The study of the external features of coal plants has not been followed so assiduously, probably because of a perplexing synonomy, and the want of books dealing with this section of the subject. As a result, the published list of coal plants is by no means complete. The great bulk of the coal flora consisted of ferns and Lycopodiaceae, the latter, however, not restricted to the coal measures, the casts of large trunks being not unfrequently found in the sand- stones of the Millstone Grits. The shale roofs of the coal seams are the chief repositories of fossil plants ; ferns, Calamites, and Lepidodendra occurring in abundance. All the under-clays or seat-rocks contain Stigmaria, whilst the roof of the Bullion Seam contains the irregularly rounded nodules already mentioned, in which, amidst a tangle of broken-up vegetable matter, are found stems, twigs, and fruit of Calamites, Lepi- dodendron, and other plants, with their minute structure perfectly preserved. In addition to the shale-roofs, plant fossils are found in some of the shales and sandstones. In some cases ironstone nodules occur in the shales containing well-preserved ferns and Lepi- dostrobi, especially in the shales under the Doe Mine of the Middle Coal Measures of Pendleton. The sandstones often contain casts of trunks and faint impressions of leaves and ferns, covered by a thin layer of carbon. Ferns are most abundant so far as regards species in the shales of the Middle Coal Measures, where they are better preserved than those of the Lower series. The stems of Calamites and Lepidodendron are also less crushed. Plant remains of any description are scarce in the Upper Coal Measures, Neuropteris and Sphenopteris being the most common. The most common plants of the Lancashire Lower Coal Measures are : — • Alethopteris lonchittca Lepidodendron obovatum Mariopteris muricata ,, aculeatum Sphenopteris Schillingsit Sigillaria elegans Lepidodendron ophiurus Trigonocarpus Parkinsoni 21