226 Notes on Post Tertiary Strata 



cent. In composition it perfectly resembles the sand of tlie 

 coast dunes, a coincidence which it is important to note in 

 discussing the origin of the formation. 



Between Portland and M'Donnell Bay there is a fringe of 

 these dunes, or sand hummocks, as they are often called, 

 extending from the sea margin to a distance of from one to 

 three miles inland. Their altitude is considerable, many 

 being 100 feet, and some even exceeding 200 feet, in height. 

 They consist simply of sand, which, first washed on shore by 

 the waves, has then been heaped up higher and higher by 

 strong southerly winds. Within their land and sea 

 boundaries flats and hollows are frequently left, and here 

 pools and small lakes of fresh water are sometimes formed; 

 or, again, the whole space is occupied by a series of smaller 

 dunes, disposed in the most irregular manner. Usually 

 there is no vegetation, and nothing meets the eye but 

 glistening masses of white sand, making a landscape of the 

 most weird and desolate character. 



The bare dunes of the coast are succeeded for a few miles 

 inland by others^ which, in the course of time, have become 

 covered with vegetation ; but their rounded outlines are stiJl 

 preserved, giving to the region where they occur an undulating, 

 billowy appearance, the contour of the land being exactly what 

 would result from the gradual upheaval of successive rows of 

 dunes, similar to those now forming on the seashore. As we 

 go farther inland the country becomes less and less undu- 

 lating, until, at a distance of 10 or 12 miles, the level plains 

 of the interior are reached. Although sand is abundant 

 here, there are no dunes, and they were either never formed, 

 or have been since entirely removed. It is most likely that 

 the coast action, which favoured the accumulation of sand 

 into dunes, did not begin to operate till after the elevation of 

 the plain country. Even in some localities where there are 

 extensive sand hummocks on the sea margin no inland dunes 

 exist ; but we may easily account for their absence in such 

 places by supposing the shore outline to have been different 

 in former times. There are indeed indications of consider- 

 able alteration in this, particularly in the volcanic region 

 around Portland, where the coast is both broken and pre- 

 cipitous, many bays and headlands having been formed by 

 inroads of the ocean. It is further evident that these changes 

 have taken place since the deposition of the earlier dunes, as 

 their consolidated remains are plainly visible amongst the 

 cliffs. 



