On the Upper Silurian Passage-beds at Linley, Salop

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Abstract
A zone of thin-bedded, often conglomeratic, sandstones, forming the passage-bed between two great formations, is frequently found to include within its series of deposits one or more hands of shell- or bone-breccia. Perhaps the most important of these zones is the one which lies between the mudstones of the Upper Silurian series and the lowest Old Red Cornstone, the most northerly extension of which forms the subject of this paper. This, from the number and variety of its organic contents, may almost be called a formation by itself. The continuance of Silurian forms of life is, however, too strongly marked to permit any division of it from that great series of deposits. On the other hand, its uppermost layers are allied, by physical constitution and fossil contents, so nearly with the overlying Old Red, that, although this new exposure at Linley adds to our knowledge of the series, it does not, in our opinion, enable us to draw a more definite boundary-line between the Silurian deposits and the Old Red Sandstone. In commenting generally upon these passage-beds, we cannot choose a more fitting preface than the following passage from ‘Siluria’:— “During the accumulation of nearly all the Silurian deposits of Britain, which were characterized by a certain fauna, the bottom of the sea was, to a wide extent, occupied by dark- and grey-coloured sediments. At the close of that period a great change occurred, over large areas, in the nature and colour of the submarine detritus. In and around the

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