10 ME. J. A. DOUGLAS OX GEOLOGICAL SECTIONS [April I914,. 



Terebratula sp. 



Most of the fossils from the black shales at the foot of the 

 Moito are considerably crushed, and, although several specimens 

 of a large Terebratuloid shell were obtained, it has been found 

 impossible to assign them to any definite species, or to say more 

 than that they are probably of Bathonian age and most nearly 

 related to a type such as Terebratula maxillata Sow. 



Ehtxchoxella sp. 



These shells, which occur usually in the form of casts, were 

 formerly referred to the Liassic species Eli. tetrahedra; if we 

 judge from the associated fossils, however, they are probably of 

 somewhat later age. and appear to possess closer affinities with 

 Hit. ohsoleta (Sow.). 



The igneous rocks of the Morro. — -Though mentioning- 

 elsewhere the occurrence of contemporaneous porphyries in the 

 Oolitic Series, Forbes, 1 when he discusses the rocks of the Morro ? 

 describes the lavas as intruded sheets. In this he is followed by 

 later writers, but the evidence summarized below appears to afford 

 ample justification for regarding their origin as contemporaneous 

 with the deposition of the sedimentary deposits : — 



(1) The whole thickness of lava exhibits typical ' pillow '-structure, the 



ovoid masses being- often more than 10 feet in diameter and lying- 

 with their long axes approximating to the horizontal. 



(2) This structure is not a phenomenon of surface-weathering, as is shown 



by its continuance through a great landslip which cuts the face of the 

 cliff , and by isolated blocks fallen on the beach. 



(3) The black shales filling the spaces between the pillows contain abun- 



dant marine fossils, which are often unbroken and well preserved. 



(4) The metamorphism of the shales has resulted in little more than the 



production of a compact hornstone selvage surrounding the indi- 

 vidual pillows. 



(5) Similar shales overlie the lava practically horizontally, and are com- 



pletely unaltered — except in the immediate vicinity of the pillows 

 (PI. m, fig. 2). 



(6) Microscopic examination of the rock of which the pillows are 



composed shows that the porphyritic constituents are set in a true 

 glassy ground-mass. This would hardly be expected to occur in a 

 subsequently intruded sheet of lava over 100 feet thick, owing to 

 which its dimensions woidd necessarily undergo somewhat slow cooling. 



(7) The mass cannot be regarded as composed of a series of thin intrusive 



sheets, which might be suggested in explanation of some of the 

 phenomena enumerated above. 



In general appearance and mode of occurrence, then, this rock 

 presents many of the characteristic features of a typical pillow- 

 lava, and seems to have differed little in its mode of origin from 

 other lavas exhibiting a similar structure. It undoubtedly represents 

 a submarine volcanic How. which took place contemporaneously with 

 the deposition of the shales in which the pillows are embedded ; 

 though whether the eruption itself was actually submarine or 

 subaerial is a moot point. The abundant individuals of the genus 



1 Q. J. G. S. vol. xvii (1861) p. 36. 



