TRANSACTIONS OF THE SECTIONS. Ill 



vestigated, of finding cliaracteristic forms, which would enable ns to place them 

 with certainty as the equivalents of the Lower Silurian rocks, so well defined by 

 Sir Roderick Mm-chison as occurring in Ross and Sutherlandshire. 



2nd. The deposits on the eastern side of the island, and skirting the shore of the 

 Sound of Islay from Ard-na-huamh on the north to Balleochreoch on the south, 

 are of Cambrian age. Although the author has not seen the precise equivalents 

 of the greenish-grey micaceous nags, with the felspathic partings found on the north 

 side of Big-Free-Port Bay, on which we find sun-cracks, rain-prints, and what some 

 suppose to be .annelid tracks or bmTOWs, yet they coincide so well with similar 

 rocks, so very clearly shown by Sir Roderick Mm-chison as occurring in Suther- 

 landshire, where their relation to the inferior conglomerates is so ably traced, and 

 also those described by the late 'Mv. Salter from the Longmynd beds in "Wales, that 

 if similarity of fossil "forms are to govern us in determining the relation of forma- 

 tions, then those stratified rocks exhibited on the shore at Big-Free-Port and to 

 Balleochreoch, folding over and suri'oimding the basic conglomerate mass, can only 

 be placed iu a similar stratigraphical position to those referred to by the above 

 able authors, thus extending our knowledge of Cambrian rocks occurring fur- 

 ther south in Scotland than has been hitherto recorded. The author quite agreed 

 with Prof. Ramsay iu supposing that these rocks were deposited in an inland and 

 freshwater lake ; and that those cracks are due to the influence of the sun is abun- 

 dantly evident. If they had been deposited in an estuary of the sea, the soft mud 

 would not have got time to crack, as each intiowing tide would have kept the 

 matrix sufficiently moist to prevent its shrinking. 



3rd. The metaraorphic rocks on the western extremity of the island, and skirt- 

 ing the shores of Lochendale for nine miles to the east, and dipping S.S.W. or 

 nearly at right angles to the plains of stratification of the preceding deposits, are 

 of Laurentian age. They differ so widely both in mineral character and strati- 

 graphical aspect from those of the central valley and eastern side of the island, 

 that there can be little doubt regarding theu' proper identification. Their litho- 

 logical aspect and mineral character coincides so well with the fundamental Gneiss 

 of Sutherlandshire, and desigTiated by Sir Roderick Murchison as of Laurentian 

 age, that we have not the shghtest hesitation in identifying those of Islay as be- 

 longing to the same period. 



4th. Iu the basic conglomerates on the eastern side of the island we have got 

 traces of striated rocks imbedded in the mass, although we are not prepared to 

 speak with any degi-ee of certainty regarding the source or direction of the materials 

 constituting the conglomerate mass. If, however, we glance at the topographical 

 aspect of the Highlands and Island, and compare the imbedded boulders of granite 

 with the granites found in situ throughout the Highlands, we feel the necessity of 

 tracing them to another source, and hope we do not overstep the bounds of prudent 

 speculation in suggesting that those erratics are the reasserted materials of some 

 great northern continent that has yielded to the ceaseless gnawing tooth of time, 

 leaving those scattered fragments as the wreckage of its former greatness, and that 

 the materials of which the mass is composed have in time, deeper than we have 

 hitherto suspected, been transported by the agency of ice. If so, then this is 

 another proof that we are not in a position to limit the agency of ice to any single 

 period of our earth's history. 



Additions to the Fossil Vertclrate Fauna of Burdiehouse, near Edinhiirf/h. 



By Prof. Teaquair. 



On the Structure of the Dictyosylons of the Coal-measures. 

 'By Professor W. C. Williamson, F.B.S. 



Professor W. C. Williamson referred to Mr. Binney's original description, in 

 186G, oi Dado.rylon Ohlhamium, and to his own subsequent paper, in which he se- 

 parated his new genus Dictyoxylon from the Dacloxylons. He then described the 

 former genus in detail, commencing with D. Oldhamium. In this plant there was 



