Lawson ] 



Geology of Carmelo Bay. 



23 



out of small calcareous shells — apparently foraminifera, an that the 

 formations of this series must have once teemed with such remains. 

 Besides the moulds of these minute shells there are in various parts 

 of the formation also numerous casts of Miocene molluscs. 



Occasionally there may be detected in this shale a few irregular 

 specks of bitumen, and the occurrence of economically important 

 deposits of this substance in the same formation, in other parts of 

 the coast, has given rise to the term "bituminous slate," which has 

 sometimes been used as a designation for these rocks. Almost any 

 specimen of the shale, however white it may appear, will yield a 

 distinct bituminous odor when heated in a closed tube, turning black 

 and then bleaching white. Besides these prevailingly chalky white 

 formations, which probably constitute over 95 per cent, of the entire 

 volume of the series, there are some other facies of the same forma- 

 tion, and a very subordinate proportion of other rocks. The shale 

 may, at a few points on the main coast road, be observed to be to a 

 very limited extent silicified and take on the appearance of silicified 

 wood. The silica is apparently chalcedonic, and has replaced the 

 shale without obliterating the shaly layers, though quite frequently 

 veins of the chalcedony cut the latter transversely. 



Apart from these local and secondary silicifications there are thin 

 beds of a dense, compact, light gray, opal-like rock. These contain, 

 like the chalky shale, numerous hollow moulds of minute univalves 

 and occasional impressions of a bivalve of the genus macoma. The 

 pores formed by these moulds in the opaline rock are not so numer- 

 ous as in the chalky facies; they are also more sporadic and are not 

 arranged in bedding planes. 



'The rock is entirely unaffected by boiling in hydrochloric acid, 

 has a conchoidal fracture, yields water in the closed tube, and may 

 be scratched with a knife like opal. The tongue adheres strongly 

 to the broken surface of the rock. Fragments of this opaline rock j 

 or, indeed, of any portion of the shaly series, whether chalky or 

 opaline, turn black when heated on a piece of platinum foil and then 

 on continued heating burn white again. This, together with the 

 bituminous odor yielded in the closed tube, indicates the presence 

 of a carbon compound distributed through the rock, and is sugges- 

 tive of the source of the asphaltum which is elsewhere found in 



