Discussion

Abstract

The A uthors ' reply: We naturally agree with Mr Hutchison that the overall relationships between acid and basic rocks are very different in orogenic zones from what they are in non-orogenic regions. We never maintained that the process of magma-production was the same for both; nor did we intend our diagram showing a possible situation in which a net-veined intrusion, a composite dyke, and a composite lava flow might originate to have any relevance to the production of syntectonic granites or batholiths with satellitic basic bodies. By our remark that we ‘did not believe that the tectonic level was as important as Dr Bishop believed’ (Blake et al. 1965, p. 45) we meant that, in our opinion, certain detailed relationships at the level represented by the igneous complex of Guernsey should not have to be given a different significance from similar detailed relationships in complexes that formed at higher levels. Specifically, we are convinced that granitic pipes in basic diorite occurring in Guernsey formed in the same way as granitic pipes in dolerite at Slieve Gullion; and that a net-veined complex in Guernsey in which the host diorite shows a progressive reduction of its grain-size against the veins was formed in the same way as certain high-level net-veined complexes having this and other features in common with it. We think that the finer-grained margins mean the same thing at the two levels. It is not clear to us what are the too-broad generalizations that Mr Hutchison says we have been tempted