8 ME. J. A. DOUGLAS (Xtf GEOLOGICAL SECTIONS [April 1914* 



pamphlet on the fossils of the Morro, and, from the supposed 

 occurrence of Illiynchonella tetrahedra, assigned to these beds 

 a Liassic age. In a later manuscript copy he alters his opinion, 

 owing to the discovery of further evidence, and places them in the 

 Oxfordian. I have to thank this author for showing me the 

 fossiliferous horizons, and putting the whole of his interesting col- 

 lection at my disposal. Among the specimens that he has sent me 

 since my return to England are a few ammonites, an examination 

 of which leaves little doubt that his later determination is the 

 correct one. (See p. 10.) 



The Morro rises almost vertically along its seaward face to a 

 height of over 450 feet, and, as its sloping sides are almost com- 

 pletely covered by sand, a correct delineation of the vertical 

 succession of the beds is a matter of some difficulty, although this 

 is a point of minor importance as compared with the estimation 

 of their age. At the base of the hill are exposed about 70 feet of 

 black and olive-green shales, dipping 10° southwards, in which 

 fossils are of rare occurrence and badly preserved. These include 

 crushed lamellibranchs (one of which suggests Qryphoea), large 

 Terebratuloid shells, and poor casts of Rhynchonella. These 

 beds become slightly more arenacous towards the top, and here 

 Senor Escutti Orrego has obtained two fairly-good specimens of 

 ammonites {Macro cephalites sp.). 



The basal shales are altered at their summit to a hard flinty 

 rock by an overlying bed of porphyritic augite-andesite, 150 feet 

 thick, and exhibiting well-marked pillow-structure (PL III, fig. 1), 

 the origin of which is discussed below. The spaces between the 

 pillows are filled up with a black shale or mudstone, slightly 

 metamorphosed, but containing in abundance well-preserved lamelli- 

 branchs (Posidonomya). This deposit is continued for a few feet 

 above the top of the first or main lava, containing fossils similar 

 to those found between the pillows and an occasional ammonite 

 (Cosmoceras sp.). 



It is succeeded by thinly-bedded, reddish, sandy shales, with veins 

 and layers of gypsum, having a total thickness of 150 feet, or 

 about equal to that of the main lava. 



Along the north-eastern slope of the Morro, towards the base of 

 this series, is seen a small sill of compact greenish-grey dolerite, 

 which has the form of a lenticular or wedge-shaped intrusion about 



9 feet thick, thinning out eastwards and altering the shales both 

 above and below it. Pillow-structure is completely absent from 

 this rock, and it differs essentially from the main mass described 

 below. 



Above the red shales more beds of pillow -lava are visible, 

 occurring at several horizons. Towards the summit appear further 

 red shales, followed by about 2 feet of impure limestone containing 

 Serpulites, badly-preserved lamellibranchs (Pecten, Modiola, etc.), 

 and occasional Echinoid spines (probably Gidaris). 



Finally, the hill is capped b} r another lava-bed, similar in nature 

 to the main mass, but of a reddish colour and much weatbered. 



