TRANSACTION.'^ OF SECTION 0. 581 



4. Rfiport on lite Erratic Blocks of (he British Isles. 



5. On a Section in a Post-glacial Lacustrine Deposit at Hornsea, 



By T. Sheppard. 



During' the past few years the various sections iu post-glacial lake-beds on 

 the Holderness coast liave disappeared, as a result of the erosion of the cliffs, 

 aud it has been exceedingly difficult to obtain details of the various beds in 

 consequence. During the spring of the present year, however, several on-shore 

 gales resulted in a sea-wall in front of the promenade at Hornsea being 

 demolished, behind which was exposed an exceptionally fine series of clays, 

 marls, peat, and gravel, representing the bed of an ancient mere. This was 

 evidently at one time beneath a sheet of water similar to the present Hornsea 

 Mere. Lists of remains of plants, fi-esh-water shells, coleoptera, >S:c., were given, 

 and the fauna and flora of the old and modern meres compared. 



G. On the Plain of Marine Demidation beneath the Drift of Holderness, 

 By W. H. Crofts and Professor P. F. Kendall. 



7. Igneous Rocks of the Districts S. W. of Do/gelly. 

 By Professor S. H. Reynolds. 



This paper described a portion of a larger piece of work upon which Mr. PhUip 

 Lake and the author have been engaged for the past ten years. The paper dealt 

 solely with the petrography of the rocks, which include the following types : — 



(a) Intrusive diabase and granophyre (eurite) ; 



(b) Contemporaneous andesite and rhyolite ; 



(c) Ehyolitic and andesitic tuft". 



The most noteworthy features are : — 



(1) The great sills or laccolites formed of a diabase devoid of olivine or original 

 hornblende. 



(2) The remarkable series of rhyolitic tuffs and of nodular and banded 

 rhyolites. 



8. A Picrite from the Eastern Mendijis. By Professor S. H. Reynolds. 



A number of loose pieces of this rock have been found by Mr, H. E. Balch, of 

 Wells, in the neighbourhood of the Ebbor Gorge. Pieces were sent to Dr. J. S. 

 Flett and the author, and were recognised as augite-picrite. Probably the rock 

 forms an intrusion in the Carboniferous Limestone, but is nowhere exposed at the 

 surface, being covered up by the dolomitic conglomerate — the basal deposit of 

 the Trias in the south-west of England. The pieces found were probably pebbles 

 in the conglomerate. 



9. On the Forms of Carbonate of Lime in Pearls and the Pearl-Oyster, 



By 3. LoMAS. 



The author has sought to ascertain the forms of carbonate of lime in pearls and 

 pearl-oyster by determination of the specific gravity and by Meigen's test. 



Specific Graiitij.— Three pearls were placed in a SoUas' diffusion-column with 

 crystals of calcite and aragonite used as index minerals. They all floated at the 

 same level, below the calcite and just above the aragonite. A flake of clear 

 transparent nacre from a pearl-oyster which had been kept in spirit was next 

 introduced, and this took up almost exactly the same position in the column. 



