on Concretions in the Tertiary Beds of the Isle of Man. 523 



bounded on the west, north and east by the sea, and on the south 

 by the mountains of Cambrian slate which occupy the greater por- 

 tion of the island. The arenaceous formation attains in some parts 

 a height of about 200 feet above the sea, though the undulations of 

 its surface prove that considerable portions of the deposit have been 

 removed by denudation. This district, comprising about fifty square 

 miles, furnishes perhaps the most extensive example in the British 

 Isles of a marine newer pliocene or pleistocene deposit. In the Isle 

 of Man the sea- cliffs on each side of this tertiary district afford a 

 good insight into its structure and composition. On the north of 

 Ramsey the cliffs average about 100 feet in height, and consist prin- 

 cipally of irregularly stratified yellowish sand, sometimes clayey, with 

 interspersed bands of gravel and scattered pebbles. The gravel is 

 chiefly composed of slate-rock, quartz, old red sandstone, granites, 

 porphyries and chalk flints, all of which occur in situ in the island 

 except the last two, which may have been drifted, the former from 

 Scotland, and the latter from the north of Ireland. About four miles 

 north of Ramsey the cliffs attain 150 feet. Here the lowest portion, 

 only visible at intervals, is a brownish clay loam, and the remainder 

 of the cliff is sand and coarse gravel, less distinctly stratified than is 

 the case near Ramsey, and containing rudely rounded boulders, some 

 of which are upwards of a ton in weight. They consist of granite, 

 and occasionally of carboniferous limestone. 



Organic remains are sparingly diffused in this deposit : Mr. Strick- 

 land enumerates twenty species. Of these five, viz. Crassina mul- 

 ticostata, Natica clausa, Nassa monensis, Nassa pliocena, and Fusus 

 Forbesi are not known in the British seas. Crassina multicostata 

 and Natica clausa are found living in the Arctic ocean, but the two 

 species of Nassa and the Fusus are unknown in a recent state*. 



* Mr. Strickland gives the following characters of three species of shells 

 found in the newer pliocene beds of the Isle of Man ; specimens of which 

 have been examined by several eminent conchologists in London, who all 

 concur in believing them to belong to extinct species. 



" 1. Nassa monensis, Forbes, in Mem. Wern. Soc, vol. viii. p. 62. Small; 

 volutions about six, rounded; suture deep ; ribs, nine on the first volution, 

 straight, rather distant, strong, subacute, and slightly oblique. The first 

 volution has thirteen, and the second six, distinct, regular, thread-like, spiral 

 striae, crossing alike the ribs and their interstices. Aperture orbicular-ovate, 

 canal very short and oblique, pillar-lip simple, outer lip with about five 

 slight marginal denticles on the inside, and an external rib slightly more 

 developed than the ordinary ribs. Total length, 7 lines ; first volution, 

 3i, lines ; breadth, 4^ lines ; angle of spire, 40°. 



" Obs. Resembles the recent N. macula, but is larger, more ventricose, has 

 fewer ribs, and the terminal rib is less suddenly developed. 



"2. Nassa pliocena, Strickland, 1843. Large; volutions about seven, 

 rath;r flat, with a distinct thread-like suture ; ribs, twelve on the first volu- 

 tion, straight, distant, rounded, very slightly oblique; the interstices flat, 

 exceeding the width of the ribs by one-half. The first volution with thir- 

 teen, and the second with about nine fine spiral striae, only visible in the in- 

 terstices, the ribs being smooth ; but this may be due to attrition. Aperture 

 ovate ; canal very short and oblique ; pillar-lip with about five obscure den- 

 ticles, and a spiral groove immediately behind the canal, continued into the 



