138 



KNOWLEDGE 



[June 1, 1897. 



part of the range may have been raised at a still earlier 

 period. 



The geographical relationship of the mountains of 

 Switzerland to the other ranges of the great Southern 

 European system is, as might be presumed, not the only 

 one. The western range, the Pyrenees — with, like the 

 Central Alps, a granitic axis on which repose Silurian, 

 Jurassic, and Cretaceous strata — is partly made up of 

 Nummulitic Limestone, the same formation that is so 

 largely represented in the Eocene portion of the more loftv 

 eastern range. It may, therefore, be concluded that the 

 same great elevatory movement which raised the Alpine 

 region of Switzerland subsequently to Middle Eocene 

 times affected also the Pyrenees ; and that this range, 

 rising in the Pic de Methou of the Maladetta Mountain to 

 a height of eleven thousand one hundred and sixty- eight 

 feet above the level of the sea, was then formed as a great 

 European range. 



Connected on the east with the Swiss Alps by the 

 Ehcetian, Noric, Carnic, and Dinaric ranges, are the 

 Balkans, which, although with a main chain extending 

 almost due east from near Sophia to the Black Sea, do 

 not consist of ranges having one general direction, but of 

 a number of mountain groups and ridges irregularly 

 radiating from the mass called the Etropol Balkans. In 

 Mount Olympus (nine thousand seven hundred and fifty 

 feet) is the highest mountain of the Balkan peninsula ; 

 but Muss-alla (nine thousand five hundred feet), at the 

 north end of the Despato Dagh or Rhodope Moimtains, is 

 the loftiest summit of the Northern Balkans — the Balkans 

 proper. It is only comparatively recently, by the 

 work of Dr. Hochstetter, that more than a very 

 general knowledge of the geology of these mountains 

 has been obtained. Their interior masses consist largely 

 of Crystalline and Metamorphic rocks, granites, and 

 schists ; and one of the principal mountains. Mount 

 Vitosh, is a mass of syenite with much magnetic ironstone. 

 The unmetamorphosed Sedimentary rocks overlying the 

 Crystalline schists are largely Cretaceous, Hippurite Lime- 

 stone being conspicuous, especially in the western 

 mountains, where Mount Dinaria is but one great bare 

 mass of this white rock. The Middle Eocene Nummulitic 

 Limestone is also an important formation, and on the 

 Despato Dagh, Miocene beds occur at a height of from 

 two thousand to three thousand feet. From this there is 

 justification for assigning to these mountains a post- 

 Miocene formation, and Elie de Beaumont gives a much 

 later age — post-Pliocene — to the Eastern Balkans. 



The Italian branch of the great Alpine system, the 

 Apennines, is joined to the lofty central ranges by the 

 Graian, Cottian, Maritime, and Ligurian Alps, and 

 stretches southwards in a continuous chain of mountain 

 ridges for six hundred miles. The Apennines are of 

 moderate elevation and culminate in Monte Corno (nine 

 thousand five hundred and seventy-four feet), the summit 

 of the Gian Sasso d'ltalia. They difler from the Alps in 

 not having a granitic and schistose axis, the great mass of 

 the range consisting of Jurassic and Cretaceous limestones, 

 though in the southern portion Crystalline ]\Ietamorphic 

 rocks appear, and in the most northern Apennines rocks 

 of Carboniferous age occur. The Secondary rocks have, 

 however, been so altered in many localities that they 

 yield a great variety of beautiful marbles, the pure white 

 saccharine marble of Carrara, of Jurassic age, being a 

 notable example. The great Cretaceous Hippurite Lime- 

 stone forms enormous mountain masses in the Abruzzi. 

 Overlying the Secondary rocks in large areas are Eocene 

 limestones and Miocene beds, and flanking the central 

 ranges are low hills of Pliocene deposits of an estimated 



maximum thickness of one thousand five hundred feet. 

 It is therefore evident that the Italian peninsula was 

 greatly depressed in Pliocene times, and that we owe the 

 Apennines as a prominent feature of Southern Europe to 

 a post-Pliocene upheaval, subsequent to which again was 

 the commencement of the formation of the volcanic moun- 

 tains Vesuvius and .Etna. 



Turning to the north, the great Carpathians form a 

 semicircle of nearly nine hundred miles, but united to the 

 Noric range of the Tyrolese Alps by the Bakony Waldauth. 

 They consist of the North Hungarian mountains on the 

 west, the Waldgebirge forming the middle, and the 

 Sieburgen in the Eastern Transylvanian region. The 

 Tatra group is an immense mountain mass at the north 

 of the bow, and gives in Gerlsdorf (eight thousand seven 

 hundred feet) the summit elevation of the whole range. 

 The Carpathians are almost without glaciers, and have 

 large masses of volcanic rocks, both trachitic and basaltic. 

 With a general granitic and schistose core, the south- 

 eastern ranges largely exhibit Pahrozoic rocks, while the 

 north-western granites are overlaid by rocks of Triassic 

 and Cretaceous age. Eocene Nummulitic limestones and 

 coal-bearing beds of Miocene age attest the extension of 

 the Central European Miocene depression to the Carpathian 

 region, and the fiual elevation of the range in post-Miocene 

 times. 



When, however, we leave the great Alpine mountain 

 system, and turn our attention to Northern Europe, ws 

 find more ancient mountains, for both the Ourals and the 

 Scandinavian ranges were high above the waters of the 

 Palffiozoic sea. The Ourals consist largely of Metamorphic 

 rocks, like most of the other great mountain ranges of 

 Europe, but these are not covered in any part by beds of 

 later date than the Carboniferous. These rocks, almost 

 horizontal and undisturbed in the plains to the east, are 

 uptilted when they reach the mountains, and are greatly 

 dislocated and contorted throughout the range ; and at 

 the base of the mountains, where the Carboniferous strata 

 begin to be inclined, the Permians are seen, but they are 

 undisturbed, and it is evident they were not affected by 

 any uplifting agency. Evidence is thus ailorded that the 

 Ourals were elevated between the commencement of the 

 Carboniferous and the close of the Permian epochs. 



The Norwegian mountains, extending the whole length 

 of the Scandinavian peninsula, appear to be very much 

 older still, for, in the opinion of the late Prof. Sir Andrew 

 Ramsay, there is sufficient evidence of their pre-Devonian 

 existence. The Scandinavian mountains may therefore 

 be considered to be the oldest of the great mountain ranges 

 of continental Europe. 



Hcttcrs. 



[The Editors do not hold themselves reapoasible for the opinions or 



statements of correspondents.] 



» 



DR. CROLL'S THEORY OF GLACIATION. 



To the Editors of Knowledge. 



Sirs, — Your notice of Dr. Croll's life in the April 

 Number induces me to ask space for a few remarks on 

 his theory of glaciation, because, to my mind, neither 

 he nor Sir Robert Ball have dealt with the real problem 

 in an exhaustive or satisfactory manner. 



We receive a little more heat from the sun in the course 

 of the year during the period of maximum eccentricity 

 than when the eccentricity of our orbit is nearly at a 

 minimum. The cumulative effect of this annual increase 

 continued for centuries would probably considerably reduce 

 the extent of our snow-c;ips or ice-caps. However, I am 



