278 SCIENCE IN SHORT CHAPTERS. 



will be likely to heat the clay matrix (itself formed mainly of ice- 

 ground basalt) to incipient fusion, and thereby render it more like 

 the basalt boulders it contains than the other clay that had been 

 less intensely heated on account of greater distance from the lava- 

 flow. 



The path leading to the ladder by which the bridge is approached 

 passes over such conglomerate, and further extensions are seen in 

 sections around. I saw sufficient in the course of my hurried visit to 

 indicate the existence of a large area of this particular formation. 



At a short distance from Carrick-a-Rede, on the way to Ballycastle, 

 the car passes in sight of considerable deposits of ordinary boulder 

 clay uncovered and unaltered. 



The blocks of basalt, etc. imbedded in this correspond in general 

 size and shape with the " bombs," excepting that some of the latter 

 have a laminated or shaly character near their surfaces. 



I regret my inability to do justice to this subject in consequence of 

 the fact that the above explanation of the origin of this curious for- 

 mation only suggested itself when hurrying homeward after a some- 

 what protracted visit to Ireland. As I may not have an opportunity 

 of further investigation for some time to come, I offer the hypothesis 

 in this crude form in order that it may be discussed, and either con- 

 firmed or refuted by the geologists of the Ordnance Survey, or others 

 . who have better opportunities of observation than I can possibly 

 command. 



Should this conglomerate prove to be, as I suppose, a drift deposit 

 altered by a subsequent flow of lava, it will supply exceedingly inter- 

 esting data for the determination of the chronological relations of the 

 glacial epoch to that period of volcanic activity to which the lavas of 

 the N. E. of Ireland are due. Though it will nowise disturb the gen- 

 eral conclusion that the great eruptions that overspread the creta- 

 ceous rocks of this region, and supplied the boulders of my supposed 

 metamorphosed drift, occurred during the Miocene period, it will 

 show that this volcanic epoch was of vastly greater duration than is 

 usually supposed ; or that there must have been two or more volcanic 

 epochs pre-glacial, as usually understood, and post-glacial, in order 

 to supply the lava overflowing the drift. 



This post-glacial extension of the volcanic period has an especial 

 interest in Ireland, as the " Annals of the Four Masters," and other 

 records of ancient Irish history and tradition, abound in accounts of 

 physical changes, many of which correspond remarkably with those 

 of recent occurrence in the neighborhood of active and extinct 

 volcanoes. 



In a paper read before the Royal Irish Academy, June 23d, 187,3, 

 and published in its " Proceedings," Dr. Sigerson has collected some i 

 of the best authenticated of these accounts, and compares them with 

 similar phenomena recently observed in Naples, Sicily, South 

 America, Siberia, etc., etc. The " great sobriety of diction, and cir- 

 cumstantial precision of statement," of names, dates, etc., which 

 characterize these accounts render them well worthy of the sort of 

 comparison with strictly scientific data which Dr. Sigerson has made. 



As we now know that man existed in Britain during the inter- 

 glacial, if not the pre-glacial period, and as so violent a volcanic dis- 

 turbance as that which poured out the lavas of Antrim and the 

 Mourne district could scarcely have subsided suddenly, but was 



