186 Dr. Jack oji the Geology and Topography 



Malayan peninsula, its parts by no means exhibit a corre- 

 sponding regularity. In this particular the greater number 

 of maps convey an erroneous idea. 



It has been ascertained that the Poggy islands, Pulo Nias, 

 and the whole of the northern coast, are laid down in Hors- 

 burg's charts considerably to the westward of their true posi- 

 tion, a circumstance which materially affects the supposed 

 breadth and form of the island : and it is singular that, with 

 the exception of Acheen Head, Bencoolen, and perhaps Flat 

 Point, there is scarcely a place on the west coast (where we 

 have had establishments for above a century) of which either 

 the latitude or longitude is exactly determined. The moun- 

 tains, for the most part, lie nearer to the western coast than 

 might be supposed from Marsden's map ; and a greater length 

 of course must, therefore, be given to the great eastern rivers, 

 which have their sources among them. It has been an object 

 of interest in our late investigations to trace more correctly 

 the course, the relative position, and true sources of these no- 

 ble streams, most of which afford safe navigation to the largest 

 vessels for upwards of a hundred-miles above their mouths. 



The basis of tlie island of Sumatra is probably primitive ; 

 granite has been found in Menangkabau and at Ayer Bangy: 

 but trap rocks are perhaps the most widely diffused ; while 

 the mountains of greatest elevation, and which stand in some 

 degree insulated, are generally volcanic. The volcanos of 

 Sumatra have somewhat a difterent character from those of 

 Java: the former generally terminating at the summit in a 

 ridge or crest ; while the latter are more exactly conical, and 

 have for the most part much broader bases. 



Commencing at the north with Acheen [respecting which 

 the mission of Sir T. S. Raffles in 1819 afforded the means of 

 adding to our information] I have merely to remark, that the 

 mountains which terminate in Acheen Head, together with the 

 adjacent island of Pulo Way, and the coast to the eastward, 

 including Pedier, Are of calcareous formation. 



Proceeding southwards along the western coast we come 

 to the Bay of Tappanooly, which forms a large and deep in- 

 dentation among the hills of the Batta country. In these hills, 

 which come directly down to the margin of the sea, as well as 

 in the small islands within the circumference of the bay, the 

 rocks consist chiefly of a fine-grained sandstone, frequently 

 striped with various shades of yellow and red. The strata are 

 in general even and regular, and but slightly inclined, occa- 

 sionally, however, exhibiting partial disturbances and undula- 

 tions. 



At Nattal, the next station to the southward, the mountains 



i-ecede 



