T. O.Bosworth— Birth of an Island near Trinidad. 159 



6. In cases where there is a relatively sudden change of motion 

 the drumlins tend to assume triangular, crescentic, and forked outlines. 



DESCEIPTION OP PLATES VIII AND IX. 



Plate VIII. 



.Sketch-map of South Donegal showing the glaciation. The drumUns, shown 

 in black, are inserted to some extent from personal knowledge of the 

 ground, but are also largely deduced from the contours of the 1 inch and 

 6 inch Ordnance Maps combined with the original drift-mapping of the 

 Geological Survey of Ireland. The areas treated in more detail in other 

 maps are outlined. At the point marked A there is a small latero-terminal 

 moraine on the hillside. Scale ^ inch to the mile. Eeproduced with 

 modifications by permission of the Controller of H.M. Stationery Ofiice. 



*-"'\ Plate IX. 



Fig. 1. View of drumlin topography from the Eoman Catholic Chapel, 



Ballintra, looking west- in the direction of the ice-motion. 

 Pig. 2. Drumlin with serrated crest viewed obliquely from the stoss end, 



Drumnacoil, near Bridgetown, one mile north of Ballintra. 

 Fig. 3. Eailway-cutting near Eossnowlagh Station. Section through drumlin 



showing upper and lower boulder-clay. The line of junction is indicated 



by the calcareous oozings due to water percolating along the upper surface 



of the compact lower till. 



IV. — The Birth of an Island near the Coast of Trinidad. 

 By T. 0. BOSWOETH, B.A., B.Sc, F.G.S. 



S some erroneous statements have appeared in the Press about this 

 interesting event, it seems advisable that the true facts should 

 be placed on record. 



Geological Character of the District. 



The shape of the Island of Trinidad is approximately rectangular 

 and conforms to its simple geological structure. Along the north side 

 is a mountain range formed of metamorphic rocks, but elsewhere 

 folded Tertiary (and occasionally Cretaceous) strata are at the surface. 

 < The anticlinal axes are some two or three miles apart, and have 

 parallel sinuous trends with a general east and west direction. They 

 have been mapped over a large part of the island by Mr. E. H. 

 Cunningham Craig, F.Gr.S., for the Government, and have been further 

 mapped and studied in detail by the writer during the past year, 

 some seven or eight distinct anticlines being now known. Some 

 of these anticlines are found to die out in the course of a few miles, 

 but two or three folds of greater importance are remarkably persistent, 

 and one at least of these is now proved to be continuous from east to 

 'west right across the island and has been mapped throughout 

 ■practically its whole lensth — a distance of over sixty miles. This 

 anticline is nearly parallel with and close to the south coast of 

 Trinidad, often being well exposed on the foreshore, but by reason of 

 its sinuosities and the irregularities of the coastline the axis of the 

 fold, though generally on dryland, is in some parts of its course under 

 the sea. Indeed, where it crosses Erin Bay it must be nearly two 

 4niles from the shore. It is in this bay that the new island has been 

 formed, directly on the line of the anticline. 



