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From a study of the sediments and pyroclastic rocks it would seem that the Lower Ordovician beds near Leenane and Rosroe were largely contemporaneous. What reasons did the author put forward for suggesting that the Rosroe Grits and the Leenane Grits were not time-equivalents?
Palaeogeographical conclusions drawn from the Lower Palaeozoic of western Ireland could not be related closely with those from other areas in the British Isles, and any evidence must therefore be based entirely on local outcrops. There was little doubt that during Ordovician times land lay to the east and deeper water to the west, as the author suggested, but in the Silurian the evidence did not appear to give such a simple picture. The author had concluded that the Silurian palaeogeography in Mayo was not greatly different from that of the Ordovician; but in north-west Galway there were several indications that land lay to the west and that areas of deeper water occurred to the east. In the Upper Llandovery, the arenaceous Annelid Grit was largely replaced eastwards by the more argillaceous Finny School Beds (the latter being absent west
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