File:The Quarterly journal of the Geological Society of London (13960355263).jpg
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[edit]DescriptionThe Quarterly journal of the Geological Society of London (13960355263).jpg |
REV. R. BARON ON THE GEOLOGY OE MADAGASCAR. 305 18. Notes on the Geology of Madagascar. By the Rev. E. Baron, F.L.S., F.G.S. With an Appendix on the Fossils, by R. B. Newton, Esq., F.G.S. (Read March 6, 1889.) .Communicated by the Director-General of the Geological Survey.. .Plates XIII. & XIV.. General Description. Madagascar is as yet almost a terra incognita to the geologist, nothing, so far as I am aware, but notices of the most fragmentary kind ever having appeared in regard to its geological features * ; and, indeed, until the country is surveyed by competent men, we must be content with descriptions of the most general character. In the absence of something more complete, I present the following; notes, drawn up from personal observation, to which 1 have added here and there a few remarks taken from other sources, as a slight contribution to our knowledge of the geology of this great island. The central portion of Madagascar is generally regarded as consist- ing chiefly of granite. Mr. Wallace, for instance, in his ' Island Life ' (p. 384), says of it : "A lofty granitic plateau, from 80 to 160 miles wide, and from 3000 to 5000 feet high, occupies its central portion, on which rise peaks and domes of basalt and granite to a height of nearly 9000 feet ; " and in the same book there is a physical sketch- map in which the whole of the interior of the island, from about 14° to 23° S. lat., is represented as an " elevated granitic region." Now if we use the terms " granite " and " granitic " in a wide and popular sense, and include in them the various members of the crystalline series of rocks, the description may be regarded as correct ; for by far the greater part of the eastern half of Madagascar consists of gneiss and other crystalline rocks, though gneiss very largely pre- dominates. Granite occurs frequently in the form of bosses and, in some places, apparently intercalated with the crystalline schists ; diorite is also frequently met with, but gneiss is certainly the pre- vailing rock. The area occupied by these ciystalline rocks, though not precisely known, reaches on the east as far as the coast : on the west it extends, in some places at least, as far as 46° E. longitude f ; and it runs in a northerly and southerly direction from about 13° 50' to 24° S. latitude. In other words, the region occupied by these crys- talline (chiefly metamorphic) rocks has a length of about 730 miles, and an average breadth of probably not less than 150, being a total area of over 100,000 square miles. Indeed it is not at all improbable that the area may cover as much as 130,000 square miles. Fully a half of the island, therefore, and that the eastern half, consists of The MS. of the present paper was prepared long before Cortese's contribu- tion in the Bollettino del R. Com. Geol. 1888, Nos. 3 & 4, was published, t Its most westerly limit is probably about 45° 50'.z2 |
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Source | https://www.flickr.com/photos/biodivlibrary/13960355263 | ||
Author | Geological Society of London | ||
Full title InfoField | The Quarterly journal of the Geological Society of London. | ||
Page ID InfoField | 36940112 | ||
Item ID InfoField | 113696 (Find related Wikimedia Commons images) | ||
Title ID InfoField | 51125 | ||
Page numbers InfoField | Pl. XII | ||
BHL Page URL InfoField | https://www.biodiversitylibrary.org/page/36940112 | ||
Page type InfoField | Illustration | ||
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Flickr posted date InfoField | 21 April 2014 | ||
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current | 05:45, 26 August 2015 | 1,166 × 2,104 (669 KB) | Fæ (talk | contribs) | == {{int:filedesc}} == {{BHL | title = The Quarterly journal of the Geological Society of London. | source = http://www.flickr.com/photos/biodivlibrary/13960355263 | description = REV. R. BARON ON THE GEOLOGY OE MADAGASCAR. 305... |
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