(front cover) James Hutton (1726-1797) was a famous British geologist who contributed to establishing modern geology. He is also known as the geologist who discovered an outcrop of unconformity and its significance for orogeny. It is located about 100 km east of Edinburgh (cover photograph). The cover photograph is a birds-eye view looking south from the top of a hill called Siccar Point, the locality of the unconformity that has been introduced twice in this Journal by Murata (1987) and Shirao (2003), respectively. The view in this photograph traces the unconformity plane to the south and the general ca. 20-degree dip of the overlying Devonian sandstone and mudstone. The underlying Silurian sandstone and mudstone dip almost vertically to show a remarkable contrast with the overlying sedimentary rocks. See also an interpreted extension of the unconformity shown in the small inset Figure 1. The unconformity plane is not a flat plane, but is an irregular plane on which conglomerate has developed, and alternates with sandstone and mudstone with a cross-lamination. From this outcrop it can be safely imagined that a large-scale orogenic movement must have occurred between Silurian and Devonian to make the flat-lying sedimentary rocks fold vertically, probably due to mountain-building in the Devonian. The timing of this orogeny corresponds to the Appalachian-Ireland-British Isles collision orogeny, which saw the Iapetus Sea consumed by Laurentia and Gondwana (W. Africa) (see review by Maruyama et al., 2011). More detailed information on the local geology is available from Cossey et al. (2004) and Barclay et al. (2005).
(back cover) A photograph of the outcrop taken as Siccar Point. It was taken behind the hill from which the photograph on the cover page was taken. The outcrop shows overlying sedimentary rocks of rhythmically alternating red sandstone and mudstone (above) and underlying cross-laminations in which conglomerate, sandstone, and mudstone are interlayered (below). Hutton's unconformity is located further down, outside the frame of the photograph.
(Photograph & Explanation: Junzo KASAHARA; Photographed on March, 27, 2011)
