L. V. Dalton — Geology of Venezuela. 203 



Fig. 2. Dionide atra, Salter. Group of portions of two individuals, broken and 

 displaced, showing external impression of parts of head-shields, 

 fragments of thorax, and the two pygidia. Upper Arenig Series : 

 Long Plantation Cutting, near Scolton, Haverfordwest, x 2. 



,, 2a. Ditto. One of the pygidia. x 3. 



,, 3. Ditto. Head-shield of another individual with part of thorax attached. 

 Same horizon and locality, x 4. 



,, 3a. Ditto. Portion of circumferential region of same specimen. x 8. 



,, 4. Ditto. Head-shield, showing border. Same horizon and locality, x 3. 



,, 4a. Ditto. Impression of same specimen, x 3. 



,, 46. Ditto. Portionof cheek of same specimen showing ornamentation, x 8. 



,, 5. Ditto. Head-shield, transversely distorted. Same horizon and 

 locality, x 3. 



,, 6. Ditto. Diagrammatic restoration of head-shield. 



III. — On the Geology of Venezuela. 



By Leonard V. Dalton, B.Sc. (Lond.), F.G.S. 



I. Intkoductokt. 



ALTHOUGH the Republic of Venezuela adjoins two British 

 colonies, only some three or four papers have been published 

 in English journals dealing with the geology of the country. These, 

 moreover, are concerned with local observations, and no attempt at 

 correlation has been made. A considerable mass of material is 

 available in Continental publications, and the author, during 

 a series of journeys through Northern Venezuela in 1910, was 

 able to collect sufficient data to form a fairly clear idea of the 

 succession of deposits, and to roughly correlate the views of different 

 writers. While more compilatory than original, the following paper 

 is offered as a basis for further study of the geology of an area so 

 closely connected with the colonies of British Guiana and Trinidad, 

 and the short bibliography includes all those papers bearing directly 

 on the subject which are known, to the author. 



From a geological point of view there are two distinct areas in 

 Venezuela between which there are few points of resemblance in 

 general character, namely, the area south of the Orinoco, commonly 

 known as Guayana, or the Guayana Highlands, and Northern 

 Venezuela. In the first we have an ancient, extremely stable, 

 land-surface, which has undergone few changes since the dawn of 

 geological history, and none at all in recent periods ; north of it lies 

 an area which has been the scene of great geological changes down 

 to quite recent times, and where numerous earthquakes still testify 

 to lack of equilibrium in the region. Since the rocks of the south 

 are all of greater antiquity than any of those constituting the region 

 north of the Orinoco, the whole series of deposits will be briefly 

 described in order, beginning with the most ancient, while the 

 various igneous rocks will be mentioned along with their associated 

 sedimentaries. 



II. Succession of Deposits. 



Wherever travellers have collected data in the Guayana region 

 they report a foundation of granite, gneiss, schist, or similar rock, 

 and where, as in the gold-bearing region of Yuruari, these 



