560 POPULAR SCIENCE MONTHLY. 



region fully accessible to observation. The proofs of the existence of old 

 volcanoes consist in part of the lavas, agglomerates, bi'eccias, and tuffs 

 erupted from the earth's interior. The walls of the orifices through which 

 these materials have reached the surface are also to be found, but often 

 more enduring than these is the column of hardened material filling the 

 once belching chimney of the volcano. Molten material that does not 

 reach the surface is often intruded from below into vertical fissures, form- 

 ing dikes, or spreads out in horizontal cavities, forming sills and laccolites. 

 Sir Archibald describes all these kinds of evidence in his early chapters, 

 and then enters upon a description of the ancient volcanic localities of 

 Britain in the order of the geological ages. The Lewisian gneiss in north- 

 west Scotland afPords glimpses of probable volcanic activity at the very 

 beginning of geological history, and there is other similar evidence dating 

 fi'om pre-Cambrian times. In South Wales a remarkably varied display 

 of British Cambrian volcanic rocks has been preserved. Coming to Silu- 

 rian time, we find a singularly complete volcanic chronicle. In Merioneth- 

 shire, Pembrokeshire, Caernarvonshire, Anglesey, the Lake District, and 

 the eastern parts of Ireland the history of eruptions is unmistakable. 

 During the Old Red Sandstone period groups of volcanoes rose in long 

 lines from the waters of most of the lakes, and threw out lava and ashes 

 over tracts hundreds of square miles in extent. Only the eai'lier half of 

 the Carboniferous period was productive of volcanoes in Britain, but vast 

 remains of these are to be seen in the puys and plateaus of Scotland and 

 in numerous dikes, sills, and bosses. After the last of the Palaeozoic erup- 

 tions ages of quiescence elapsed before volcanic activity recommenced in 

 Tertiary time. Remains of Tertiary volcanoes are to be found chiefly in the 

 isles of Skye and Mull and in northeastern Ireland. In summarizing the 

 studies here presented our author calls attention to the distribution of the 

 ancient volcanic eruptions along the western margin of the European con- 

 tinent, thus conforming to the tendency of modern volcanoes to range 

 themselves along continental borders. From Archaean time to the Ter- 

 tiary volcanic activity was remarkably persistent in the British Isles. It is 

 evident from a study of the British examples that where no fissures existed 

 in the visible part of the earth's crust communication from the internal 

 magma to the surface was effected in hundreds of instances by explosions 

 which blew out an orifice. Besides the manner in which the vents were 

 formed, the kind of materials ejected, the mode of closing of the chimneys, 

 and the manifestations of the final efforts of the volcanic force are all to be 

 read in the grand chronicle of the rocks. Seven colored maps and nearly 

 four hundred figures illustrate the work. 



"^Hiile polar auroras may be classed among the more spectacular phe- 

 nomena of the heavens, they do not force themselves upon our attention as 

 storms, lightning, shooting stars, and eclipses do. They have been studied 

 only under difficulties, for they do not occur frequently in temperate re- 

 gions as lightning does, and the time when preparations should be made to 

 observe them can not be foretold as with eclipses. It is interesting to have 

 laid before us, in the latest volume of the International Scientific Series, 

 the knowledge that has been gained in the face of such obstacles.* Much 



* The Aurora Borealie. By Alfred Angot. International Scientific Series, Vol. LXXVII. New 

 York : D. Appleton & Co. Pp. 264, liJmo. Price, $1.75. 



