TRANSACTIONS OF SECTION C. 649 



rocks of all sizes, from mere fragments to large masses several tons in -weight. 

 Most of these stones are subangular, and well striated ; a few are rounded, and 

 others are unworn and angular. In the clitFs four miles south of Aberystwith, this 

 formation occupies an old river-bed in a former valley, who-e western hill-boun- 

 dary has been destroyed by marine denudation ; also the rock here has been eiiten 

 away by streamlet and pluvial denudation into fantastic gorges and columns, some 

 of the latter being true earth-pillars, like those of 13otzen in the Tyrol. Moraines 

 are of common occurrence, but they consist of more clayey material than usual, 

 ■which results from the argillaceous character of the surrounding rocks. In some 

 cases they occur at the foot of lakes. 



Erratic blocks are abundant, occurring at heights above 1,000 ft. They are 

 often found along the sides of valleys, where they appear to have been stranded 

 after being launched off from the sides of the subsiding glaciers. All are 

 local rocks, and it is only in the extreme north and .south that boulders from 

 beyond the present drainage-areas occur. In the Llyfnant valley, S.W. of Ma- 

 chynlleth, huge boulders of felsite from the Cader Idris and Aran range of moun- 

 tains are found, they having been carried over the pass by the North Wales ice, 

 -which overflowed beyond the Dy ti valley. In the south the Teifi valley at Cardigan 

 -was invaded by a large glacier, whose birthplace -was in the mountains of Caer- 

 marthenshire. I^akes and lakelets are abundant, especially on the higher plateaux. 

 They are all rock-basins, mostly shallow, and of irregular outline. One of them 

 (Llyn Llygad Kheidol) was apparently ice-formed ; the rest cannot be. These evi- 

 dences show that Central Wales was covered with snow and ice during the Glacial 

 period; but all the glaciers of which we have any traces were of strictly local 

 character, each confined to its own drainage-area in the present valley system. 

 There is no evidence of any great mer de ylace, or of any marine submergence in 

 recent geological times. 



6. On sovie points in the Morphology of the Hhahdojjhora. 

 B[i John Hopkinson, F.L.S., F.G.S. 



Professor McCoy (' Brit. Pal. Foss.' 1854) speaks of transverse diaphragms at 

 the base of the calycles (hydrothecce) of certain graptolites, dividing the calycles 

 from the common canal or perisarc. No further allusion appears to have been 

 made to the presence of any diaphragms or septa until, in 18G8, the author 

 mentioned (' Journ. Quek. Micr. Club,' vol. i.) having observed ' an impressed line 

 between the hydrothcCEe and the periderm' (perisarc), which was compared with 

 that 'at the base of the hydrothecae in the Sertulariadte.' 



More recently Professor AUman (' Mon. Tubularian Ilydroids.' 1872), not 

 admitting the presence of any septum or constriction, has compared the calycles of 

 the Rhabdophora to the nematophores of the Plumularidaj. 



A few days ago the author examined an extensive collection of graptolites made 

 by Mr. W. Kinsey Dover, of Keswick, from the Skiddaw Slates, amongst which 

 are a few specimens showing internal structure, most clearly defined in Didi/mo- 

 (/raptus nitidus and patuhis, and Tetrcujraptus serra. In several specimens of these 

 species (exhibited) the thecas are seen to be separated from the perisarc by a dis- 

 tinctly-marked septum which seems usually to form a right angle with the theciie. 

 The perisarc is, moreover, in specimens of all the three species, seen to be 

 jointed, or crossed by transverse septa, there being one septum to each tbeca. 

 The appearance is therefore that of a common perisarc divided into chambers, from 

 each of which a single isolated hydrotheca is produced. 



These appearances are not confined to the graptolites of the Skiddaw Slates, 

 having been noticed by the author in well-preserved specimens from the Ludlow 

 rocks, and it is believed to be owing to the imperfect state of preservation in which 

 graptolites usuallj' occur that they are not more frequently seen. The true inter- 

 pretation of the appearances presented is believed to be that the septa which seem 

 to completely cut off the thecse from the perisarc, and the sections of the perisarc 

 from each other, only partially do so, as in the recent Thecaphora ; and the author 

 concluded that these specimens show that the calycles of the graptolites are true 



