454 Transactions. — Geology. 



The blue clay rests upon a layer of pumice, wLicli seems hardly to have 

 been noticed by previous observers, but which is quite as worthy of attention 

 as the blue clay itself. At Shakespeare Cliff the pumice bed is very thin 

 indeed, but it extends along the bank of the river from the mouth for several 

 miles up, varying from three to fifteen feet in thickness, and underlies the 

 town. It becomes conspicuous on the east bank, a short distance north of 

 Shakespeare Cliff, running parallel with the outcrop on the west bank, and 

 gradually swells in thickness until, between three and four miles from the 

 town, it becomes a component part of a cliff 100 feet high, and is filled with 

 fossil shells. The section here discloses a layer of red volcanic mud, stratified, 

 upon which lies from fifteen to twenty feet of pumice, reduced to lapilli, and 

 forming a tuff, with coarse sand of nearly pure quartz, and an abundance of 

 recent fossil shells of apparently the same age as those in Shakespeare Cliff, 

 but quite different in character. Turritella and Pecten^ so plentiful in the 

 latter place, seem entirely absent, while Ostrea is scarce. Dosinia and Venus 

 are prevalent, as on the modern sea beaches of the neighbourhood, with 

 Buccinum, and large species of Fusus and Voluta. A fine Crejndula and a small 

 Solarium are characteristic. These fossils are very fragile, crumbling to pieces 

 in the hand, just as if they had been burnt in a kiln. Upon the pumice is 

 superimposed sixty feet, or thereabouts, of mixed volcanic mud and lapilli, 

 which, being weather-worn, presents a curious appearance. 



It would seem that this spot was once the site of a submarine volcano, from 

 which the lower bed of pumice was ejected. The pumice slopes at an angle of 

 45° up the river, i.e., northward, but it is clear this is not the result of 

 movements from below, since the mud bed upon which the pumice rests is 

 horizontal and undisturbed, which would not have been the case had it been 

 upheaved by a movement which tilted the pumice into its present position. 

 This mud stratum, and the stratum of mixed lapilli and mud above the 

 pumice, are both destitute of fossils, although the tuff abounds with them, 

 calcined as just described, and confusedly intermingled with the pumice, 

 showing that they were hurled from their original bed into their present 

 position with the pumice itself. The upper and non-fossiliferous stratum 

 must, I apprehend, be referred to a later volcanic eruption. 



"What I have called volcanic mud is generally spoken of as ordinary clay, 

 but a cursory examination will show it to be a volcanic product ; tlie mere 

 fact that beds of it perfectly destitute of fossils lie between beds of other 

 composition richly endowed with remains of animal life is convincing. We thus 

 gain an idea of the immense volcanic discharges, extending over a vast period 

 of time, which must formerly have taken place in this region, and which, 

 indeed, can only bo said to be pretermitted at the present moment, seeing 

 that the distiict lies within the range of the yet smouldering volcano of 



