364 



the course of deposition around such vents, and were thus included. 

 The author has not failed to show that the original features of the 

 bed of the sea, of the period of eruption alluded to, have been obli- 

 terated by subsequent denudation; and I may suggest that this cause 

 has often prevented geologists from recognizing the analogy of 

 trappean phaenomena to those of submarine and insular volcanos 

 now active. 



In another communication Mr. De la Beche informs us that the 

 " Cornish grauwacke," in which term he here comprises the slates 

 of that country and their associated sandstones and conglomerates, 

 contains in some places organic remains. Specimens of these fos- 

 sils have been presented by him to our inuseum. He also states 

 that this greywacke formation, which extends into Somerset and 

 Devon, is older than Mr. Murchison's Silurian system, and may be 

 subdivided into natural sections, coinciding perhaps with some ob- 

 served by Professor Sedgwick in the Cambrian group. The slates 

 of Tintagel, long since known to be fossihferous, belong to the same 

 age as this greywacke of Cornwall. 



A joint paper by Professor Sedgwick and Mr. Williamson Peile 

 has made us acquainted with the carboniferous limestone flanking 

 the primary Cumbrian mountains, and with the coal-fields of the 

 north-west coast of Cumberland. These carboniferous strata rest 

 vmconformably on the primary Cumbrian slates. The carboniferous 

 series is divided into four groups : 1st, The great scar limestone; 

 2nd, Alternations of limestone, shale, and coal ; 3rd, Millstone 

 grit ; 4th, Great upper coal formation. It appears that the struc- 

 ture of the carboniferous limestone is nearly the same as that of the 

 Yorkshire chain so admirably described by Professor Sedgwick in 

 the first part of our fourth volume just published. 



Mr. Griffith, who has for so many years been preparing a geologi- 

 cal map of Ireland, has described to us the position of some veins of 

 syenite which traverse the mica-slate and chalk near Fair Head in the 

 county of Antrim. The syenite is composed of dark green crystal- 

 lized hornblende and brownish red felspar, with occasional grains of 

 quartz ; and the chief point of interest consists in the circumstance 

 that the syenitic veins have the appearance in general of being regu- 

 lar beds in the mica-slate, being for the most part conformable both 

 in strike and dip. They are found, however, when more closely 

 examined and traced for some distance, to deviate from the strati- 

 fication of the mica-slate, and to have an indented and saw-like edge 

 at their junction. Similar syenitic veins also penetrate through the 

 chalk in the neighbouring part of the coast, and near their contact 

 with the chalk nodules or spheroidal masses of syenite are occa- 

 sionally observed so isolated and surrounded by chalk that had not 

 the intruding veins clearly proved its posteriority, the syenite might 

 be mistaken for the older rock, rounded fragments of which had 

 been imbedded in the calcareous stratum. These phaenomena 

 remind us of the isolated nodules of granite which in Cornwall, 

 the Valorsine, and other countries, occur in the immediate vicinity 

 of granite veins. 



