134 O. S. Kinahan — Laccolites. 



1. Forest-bed on stream-tin gravels = great forest growth: land of wider extent 



than now. 



2. Marine and estuarine beds in stream -tin sections = submergence of land and 



entombment of trees. 



3. Trees and forest-bed in upper part of stream-tin sections, and, probably, sub- 



merged forests on foreshore = elevation of land, and re-advance of trees. 



4. Beds above 3 = partial submergence. 



In the above synopsis Mr. Geikie advocates a recent oscillation 

 by which the dwindling forest growth gained new strength in a 

 comparatively brief respite prior to its final decay ; and is inclined 

 to regard the traces of vegetation on the foreshore as relics of the 

 re-growth of the trees upon sites rendered untenable by the previous 

 subsiding movement. 



To this I have no objection whatever to urge : on the contrary, 

 it is in conformity with the oscillation advocated by Mr. Godwin- 

 Austen, to account for planed rock reefs at a little above high-water 

 lever (Rep. Brit. Assoc, for 1850, Trans, of Sects, p. 71). "Such 

 an oscillation might serve to explain the river sediments gaining 

 on the marine in estuarine stream-tin sections, and to enable them 

 to continue, pari passu, with a resumption of the subsiding move- 

 ment," etc., etc. (Pleistocene Geology of Cornwall, Part V. General 

 Notes, Geol. Mag. for July, 1879). 



Mr. Geikie's conclusions are based on an extensive knowledge of 

 facts, collated from all quarters, and which, I need hardly say, were 

 beyond my range. I could only advocate the probability of an 

 oscillation of a few feet, as suggested by Mr. Godwin-Austen, so 

 til at from so restricted a point of view I could not regard the 

 re-elevated foreshore as favourable to the growth of trees. I do 

 not, however, think, as regards Cornwall, Devon, and Somerset, that 

 the elevation hinted at might not, without militating against facts, 

 be made sufficiently elastic to have converted the shallows of such 

 coasts as Mounts Bay into dry land, and have continued long enough, 

 not only to arrest the decay of the surviving forests in inland 

 localities, but even to permit of their re-growth iipon deserted 

 foreshore sites, and to give colour to the tradition of " Caraclowse 

 in Cowse, in English the hoare rock in the wood," as applicable to 

 St. Michael's Mount. 



In conclusion, I must plead necessity for recurring at such length 

 to this subject, at the same time expressing my thanks to Mr. Geikie 

 for affording me the opportunity of explaining, more fully, views 

 which the general tenor of my classification, as expressed in my 

 papers on Cornish Post-Tertiary Geology, may have left somewhat 

 ill defined, as it was foreign to my purpose to discuss at length the 

 changes indicated by the details of individual stream-tin sections. 



VI. — Laccolites. 



By G. H. Kinahan, M.E.I.A., 



President of the Eoyal Geological Society of Ireland. 



IN the Eeport on the Geology of the Henry Mountains, Eocky 

 Mountain Eegion, Mr. G. K. Gilbert, of the U.S. Geographical 

 and Geological Survey, points out that many of the intrusions of 



