58 



of Mount Eckersley, at an elevation of 319 feet (see section, 

 fig. 2), there is an outcrop of limestone, which I take to be an 

 outlier of the Portland beds. By adding this height to the depth 

 of the Hey wood bore, 190 feet below sea level, we get a vertical 

 thickness of 509 feet, but as the base of the formation is not then 

 reached, it is impossible to say how mucli lower^ the strata ex- 

 tend. 



The Muddy Creek tertiaries, and, for the most part, those tO' 

 the south of them, right down to the sea coast, are overlain by 

 basaltic rocks. On the Glenelg, and in the country to the west 

 of it, these are absent, and the tertiaries there are sometimes 

 seen on the surface, though they are usually covered by drift 

 sand. 



Many of the vents, through which the lava sheets have issued, 

 are still rejDresented by volcanic cones of moderate height, as 

 Mounts Bainbridge, Pierrepoint, Napier, Eccles, Eckersley, &c. 



The Portland Bay beds were probably covered by an outflow 

 from the extinct crater at Cape Bridgewater. Some of the lava 

 overlying the Muddy Creek beds may have come from eithei 

 Mount Bainbridge or Mount Pierrepoint, extinct volcanoes about 

 seven miles distant. A portion of it, however, was probably 

 ejected closer at hand. Mention has before been made of the 

 miniature falls over which the Muddy Creek flows, just before 

 its junction with the Grange Burn. Here massive basaltic rocks 

 extend right across the stream, completely concealing the 

 fossiliferous strata, which do not appear again till the junction is 

 passed. A few chains from the falls, on the north side of the 

 creek, there is a low conical hill, with a ring of basaltic boulders 

 surrounding it, and there can be but little doubt as to this being 

 the spot from which the lava in the immediate vicinity proceeded. 



Wherever seen, from Portland to the foot of the Serra Range^ 

 the basalt is essentially the same rock, viz., a true dolerite, with 

 olivine, triclinic felspar, and augite as its chief constituents. 



The age of this rock is, I am aware, a moot point, some assign- 

 ing it to the pliocene and others to the pleistocene period. I 

 prefer to regard it as not older than pleistocene, for the following 

 reasons : — 



1. The lava flows from Mounts Napier and Eccles are even 

 now most striking features of the landscape, looking like rivers 

 of stone, as they wind along over miles of country, till they reach 

 the sea coast, while the rocks still present such sharp angles that 

 to attempt to walk over them would cut the stoutest boots to 

 pieces in a few hours. Even supposing these to be of later date 

 than the others mentioned, the difierence of age cannot be great, 

 tertiary fossils being alike found under all the basalt from Port- 

 and Bay to Muddy Creek. 



