June, 1909] THE VICTORIAN NATURALIST. 21 



along a slight depression in the surface of the newer basalt of the 

 plains, and may be crossed by the railway bridge or road bridge, 

 or often for the greater part of the year by a natural basaltic ford. 

 If the railway line be followed for a very short distance from the 

 creek two small cuttings will be seen, the first through basalt, 

 with its typical black clay soil, whilst the second displays a good 

 section of the sandy shell-beds. This section is about two and 

 a half miles from the North Williamstown station and about a 

 quarter of a mile from the present shore line. 



This spot serves well to show how fossils may be preserved, and 

 a little study of the conditions will well repay those who investi- 

 gate them. At first sight the shell-beds appear to show horizontal 

 layers, but a closer inspection shows false bedding to be distinctly 

 present. In some parts the beds are largely composed of layers 

 of fine, loose sand, with varying quantities of shells, whilst other 

 layers are almost entirely shells. The porosity of those sandy, cal- 

 careous beds is well shown by the hardening of certain layers by 

 the deposition of a limy cement, and the consolidation towards 

 the surface, with the development of a travertine, shows the part 

 which evaporation has played in the changes through which these 

 beds have passed. By careful collecting a large series of fossils 

 may be obtained from this section, including something upwards 

 of a hundred different species of MoUusca, apart from remains of 

 Crustacea, Polyzoa, Corals, Echinoids, and Foraminifera. 



An examination of these various specimens proves them beyond 

 doubt to be all living species, and the age of the deposit can, 

 therefore, only be considered as geologically recent. Although 

 many of the shells retain their colour markings distinctly enough, 

 one cannot help being struck by the fact that a considerable 

 number show a bleached and corroded appearance, but this is 

 not to be wondered at when it is understood that these very 

 shells have contributed to the calcareous cement now noted 

 through the beds. With regard to the organic remains, there is 

 no hesitation in saying that they are marine, but occasionally 

 a layer of brackish water shells, composed of such genera 

 as Truncatella, Coxiella, Assiminea, Salinator, and Ophicardelus, 

 make their appearance, and for such alternations we must be 

 able to account in a reasonable manner. 



It is generally known that the basalt of the plains has a 

 gradual slope seawards, and that the lava flow actually runs out 

 for a considerable distance below the present sea level, but the 

 reason for this is perhaps not so well understood. The evidence, 

 which can be gathered readily enough, shows that the lava must 

 have been a terrestrial flow, and, consequently, its present position 

 can only be explained by a general subsidence, which, without 

 doubt, followed as a natural sequence to the volcanic outpourings. 

 The basalt has suffered very considerably by marine erosion, 

 especially as there has been an abundance of grit derived 



