TRANSACTIONS OF THE SECTIONS. 75 



or a group of shells — generally spiral univalves — all of well-known Devonian forms. 

 The organic structure is frequently preserved on the inner or concave surface of the 

 enveloping ei-ust, even when the nucleus is reduced to powder. Occasionally organic 

 traces are discernible on the exterior surface of the chalcedony, but such cases are 

 not frequent. Some of the nuclei are slightly siliceous, but in no. case more so than 

 ordinary limestones are. 



Beekites which have fallen from the cliff, and have been for some time exposed to 

 the action of the waves, are much abraded, while those taken at once from the rock 

 above the reach of the sea have not the least marks of friction ; hence it may be 

 inferred that the chalcedony has been deposited on the nuclei since they became 

 immoveable, that is since the conversion of the ancient triassic sea-beach into a 

 conglomerate rock. 



Beekites are found in every part of the Torbay conglomerates, which extend along 

 the coast from two and a half to three miles, but they are considerably more abun- 

 dant at Livermead Head, and at and near Paignton harbour, than elsewhere in the 

 district ; but though rocks of the same age and character prevail throughout a great 

 part of the south-east of Devonshire, no Beekites have been found beyond the district 

 named ; indeed, so far as is at present known, they appear to be peculiar to Torbay. 



On whatever surface chalcedony is deposited, it appears in most cases to take a 

 tubercular arrangement ; hence the tubercles on the surface of the Beekite. From a 

 careful examination of all the facts of the case, it seems probable that after the forma- 

 tion of the triassic conglomerate some of the calcareous pebbles in it underwent 

 decomposition ; that water holding chalcedony in solution, and passing through the 

 rock, deposited the chalcedony on the nucleus : the nucleus in some cases continued 

 to decompose, by which it was wholly or partially detached from its envelope, and 

 not unfrequently reduced to dust. Suppose the decomposition to have commenced 

 at various points or centres on the surface of the pebble, the chalcedony deposited at 

 these points would form central tubercles; let the decaying process extend from and 

 around these centres, the chalcedony deposited around each tubercle would form a 

 ring ; in like manner a succession of rings might be formed, until they touched, after 

 which a more comprehensive circle might invest two or more of the systems already 

 formed, until the whole surface would be covered. 



On the Correlation of the North American and British Paleozoic Strata. 

 By Professor H. D. Rogers, Boston, U.S. 



On the Origin ofSaliferous Deposits. By Professor H. D. Rogers, Boston, U.S. 



On the Great Pterygotus (Seraphim) of Scotland and other Species. 

 By J, W. Salter, F.G.S., of the Geological Survey of Great Britain, 



This paper was in some measure a continuation of one published in the Quarterly 

 Geological Journal for 1855, describing some new and large crustacean forms from 

 the uppermost Silurian rocks of the south of Scotland. 



They were described under the name of Himanthopterus, and were supposed to 

 differ from the published fragments of the great Pterygotus by the lateral position of 

 the large simple eyes. 



In the general shape of the body, however, the terminal joints and tail, in the want' 

 of appendages to the abdomen, as well as in the form and number of the swimming 

 feet, mandibles, maxillae and antennae, there was found to be on further examination 

 the closest resemblance between Himanthopterus and the great Pterygotus. And the 

 resemblance has been carried still further by the favourable collocation of all the 

 known specimens from the Scotch collections, which have furnished nearly all the 

 portions ; and also the head. This is now found to be exactly like that of Himan- 

 thopterus, and to have lateral, not subcentral eyes, as represented by other authors. 



The two genei-a are therefore identical, and the group, as now constittited, includes 

 a number both of small and moderate-sized Crustacea, along with some which were 

 far larger than any living species, and which certainly attained a length of six or 

 eight feet. 



