154 NATURAL SCIENCE. ^^■■ 



fact which led De CandoUe to regard it as a series of incipient 

 species ; for if the connecting forms died out, leaving some varieties 

 more isolated than at present, the latter would be at once ranked as 

 species. From the evidence of their fossil remains, together with the 

 facts of their present distribution, "it is at least exceedingly probable 

 that the European oaks, including our English oak, came into exist- 

 ence somewhere in the East, and that, after spreading from Asia 

 towards the West, they are now slowly retreating before competing 

 forms — e.g., the beech." 



A Short and Concise Account of the Eruptive Phenomena and Geology of 

 Monte Somma and Vesuvius, in Explanation of the Great Geological 

 Map of that Volcano constructed during the Years 1880 to 1888. By 

 H. J. Johnston-Lavis, M.D. Small Svo. Pp. 21. London : George Philip and 

 Son, 1891. 



Probably every geologist who has toiled over the rugged surface of a 

 Vesuvian lava stream, or has tried to thread his way through the 

 tortuous paths between the vineyards of its lower slopes, has felt the 

 need of a geological map of the volcano and its immediate environs. 

 Perplexed, moreover, by the intricate mingling of ashes, tuffs, lavas, 

 and dykes belonging to different periods and eruptions, he has 

 probably also longed for a work that would be more detailed than 

 Lobley's and more modern than Phillips'. One of these desiderata 

 has now been supplied by Dr. Johnston-Lavis's splendid large-scale 

 geological map, and the other is promised shortly as a monograph of 

 the mountain of which the pamphlet named above is a preliminary 

 sketch. The map is on a scale of i to 10,000 (6^ inches to the mile) : 

 it is issued in sheets, each measuring 30 inches by 20. It is well 

 printed and coloured, and its topography is more accurate than that 

 of the Itahan map on which it seems to be based. The colouring 

 adopted contains some novel methods to express the slight variations 

 in the nature of the soil which cause so marked a difference in its 

 agricultural value. To assist reference from the monograph, the 

 author has called several previously unnamed valleys after geologists 

 who have worked on Vesuvius. Exact reference to the numerous 

 dykes on the wall of the Atrio are now possible, as they have been 

 marked by the great white numbers which tourists on the summit of 

 the crater generally seem to mistake for advertisements. In the 

 pamphlet accompanying the map. Dr. Johnston-Lavis gives a short 

 sketch of the history of the volcano, and this he divides into four eras 

 and nine phases, of which the first six were prehistoric. In the first 

 era Vesuvius was an island, and probably ejected lavas of a more 

 basic type than any formed in later times, and from which leucite was 

 absent. In the second era the great mass of lavas, scorias, and ashes 

 which now form the lofty precipitous wall overhanging the Atrio del 

 Cavallo were produced. The third era commenced by a long period 

 of inactivity, and ended by an explosive eruption, after which there 

 was a series of eruptions, with periods of repose. The first historic, 

 or the Plinian eruption of A.D. 79, occurred in this era ; it destroyed 

 Monte Somma and began to build the existing cone of Vesuvius a 

 little to the south of the original centre of eruption. The last era 

 began with the terrible eruption of 163 1. A short account is given of 

 the surface erosion, of which that performed by the moyas or mud 

 streams of the northern slopes of Monte Somma is the most distinctive 

 feature. 



