Geological Society of London. 287 



of worms allied to the recent Sabellarice. ; but they are liable to be 

 mistaken for Algge of the genera Palceophycus and Buthotrephis. 



Some large cylindrical bodies from the Potsdam Sandstone are 

 described as having been supposed to be trunks of trees ; but the 

 author regards them as probably concretions formed around slender 

 stems, like some now forming in the alluvial mud of the St. Lawrence. 



Some curious combinations of worm-tracks with ripple-marks 

 and shrinkage-tracks are described ; as also branching or radiating 

 worm-trails, which present some resemblance to branching Fucoids. 

 Finally the author described the formation of rill-marks on the 

 mud-banks of the tidal estuaries of the Bay of Fundy, and indicates 

 their identity with some impressions in slabs of rock which have 

 been described as Fucoids under several generic names. 



4. "Contact-alteration at New Galloway." By Miss M. I. 

 Gardiner. Communicated by J. J. H. Teall, Esq., M.A., F.G.S. 



A description is given of an alternating series of grits and shales 

 occurring at the eastern end of the northern edge of the Cairnsmore 

 of Fleet granite-mass. The rocks here are generally more altered 

 than around other parts of the granite margin. The author describes 

 a transverse section about half a mile from the granite, and traces 

 the changes which occur in the rocks when passing towards the 

 granite. She notices (1) the extreme variation in the amount of 

 alteration in different places, but at the same distance from the 

 granite ; (2) the entire recrystallization, in one locality, of the 

 shales for about 2 feet and of the grits for about 100 yards from the 

 granite margin ; that material seems to have travelled through 

 the rock, so that the most altered grit largely consists of crj'stals, 

 here of one mineral, there of another, as though material had been 

 conveyed from one part of the rock to another to form small 

 nests ; (4) the apparent order of succession of the minerals, garnets 

 rarely containing anything but colouring-matter and quartz, chiasto- 

 lite containing garnets, and bands of mica sweeping round both ; 

 (5) evidence which appears to the author to indicate dynamic meta- 

 morphism, as furnished by the sigmoidal folding of knots in the 

 shales and by the appearance of phenomena suggesting thrust-planes. 



The author considers, however, that the main metamorphism is 

 due to the intrusion of the granite, and that the variation in the 

 amount of alteration at the same distances, the mode of alteration 

 of the grits, and the transference of material might be accounted 

 for by the passage of highly heated water. Other evidence points 

 to the changes having been brought about slowly. 



Among the minerals produced in the contact-zone are secondary 

 quartz, felspar, brown and white micas, chiastolite, sillimanite, and 

 garnet, their modes of occurrence being described in detail, in rocks 

 of various degrees of alteration up to those in an abnormally high 

 state of alteration near the granite, which resemble rocks of doubtful 

 origin in other localities. 



