The Geolo<ji/ of Coinuiuhd. 187 



Besides these many other boulders over 2 feet in diameter 

 occur. One large fragment l3'ing in the creek appears to have 

 formed part of a glaciated surface, as the scored part is so well 

 rounded, in contrast to the usual glaciated stone which is flattened 

 where scored. 



In the more unstratified mudstones the boulders and pebbles 

 though nunierous are as a rule small and well worn and show no 

 trace of arrangement in the matrix, whereas in the stratified 

 mudstones, as already remarked, a certain amount of arrangement 

 is to be observed occasionally. 



It is of importance to observe the more striking varieties of 

 rock material among the boulders for the purpose of tracing their 

 origin if possible. Many quartzites for example occuiTing in the 

 drift would ))e difficult to trace to their source with any degree of 

 certainty, but other kinds of rock may be of considerable value in 

 this respect. Among such may be mentioned the various granites, 

 gneiss, a felspar porphyry with a dark green ground mass 

 containing red felspar crystals, certain quartz porphyries and a 

 mica-diorite not unlike the Warburton trap rock. The granite 

 most commonly niet with is very coarse, some of the felspar 

 crystals being several inches long. Besides the I'ocks above 

 mentioned the included material consists of slate and quartz 

 (probably derived from the local Silurian rocks) jasper, lydian- 

 stone, greisen, conglomerate sandstone, grit and two blocks, one 

 18" in diameter of niarcasite, in a tine-grained quartzitic matrix. 

 We have to thank IMr. Walcott, F.G.S., of the National Museum, 

 for kindly examining this specimen. 



During a visit to Springhurst, about two years ago, one of the 

 authors observed several types of rock in the glacial drift there 

 which we have not found in the Bacchus Marsh district. Among 

 such may be mentioned a f i-equently occurring porphyry, with a 

 slate-colored matrix, containing small crystals of quartz and a 

 little felspar, a very red granite, and agatoid and jasperoid 

 quartz. Boulders also of sandstone crammed with fossil casts 

 of brachiopods, etc., are also frequent in this district. ^Ir. 

 Etheridge, to whom one of these boulders was shown, said they 

 might be Upper Silurian or Devonian. 



We mention Springhurst in this connection as tending to show 

 that certain kinds of rock may be confined more or less to a 



