91 



THE GEOLOGIST. 



on 



the nature of calcareous deposits, and on the contemporaneity of certain 

 groups of der^osits, dependent on the oscillatory movements of land and 

 sea, the author described his plan of sho^ ing on maps the relative thick- 

 nesses of the two classes of strata under notice, by means of isodiametric 

 or isometric lines (properly isopithic, or indicative of ec[ual thickness of the 

 strata). 



jTjo-. 2. — Distribution of tBe Calcareous and Sedimentary Stj-ata of the Great 

 Oohte, Oxfordshire. 



Mr. Hull then proceeded to show the application of the isodiametric 

 system of lines to the Carboniferous strata of the midland counties and 

 north of England ; showing that there is a south-easterly attenuation of 

 the ar(jillo- arenaceous strata, and a north-westerly attenuation of the cal- 

 careous strata. The existence, in the Carboniferous Period, of a barrier 

 of land crossing the British area, immediately to the north of lat. 52°, was 

 insisted upon ; and, although this barrier was probably broken through (in 

 South Warwickshire) in the latter portion of that period, yet it divided, 

 in the author's opinion, the coal-area into a north and a south portion, the 

 latter showing a very different set of directions in the attenuation of its 

 strata ; the shales and sandstones thinning out eastward and the lime- 

 stones in the contrary direction. 



In conclusion, the author stated his opinion that the source of the 

 Carboniferous sediments was in the ancient North Atlantic Continent, for 

 the existence of which Lyell, Grod win- Austen ^ and others have argued ; 

 and he inferred that the shores of this Atlantis, composed principally of 

 granitoid or metamorphic rocksj were washed on the west side by a current 

 running south-west which drifted the sediment in that direction; and, on 

 the other, by a current running south-east which carried sediment over 

 the submerged British area. 



Geologists' Association. — Fehriidry 3- — Professor Tennant, F.G.S., 

 President, in the chair. The following paners were read : — 1. " On the 

 Cretaceous Group in Norfolk." By C. B. Eo'se, Esq., F.G.S. The author, in 

 an elaborate paper, described the general divisions of the chalk formation 

 as exhibited in Norfolk, and following the arrangement proposed by the late 

 Mr. AVoodward, he divided the beds into Upper Chalk. Medial Chalk, 

 Hard Chalk, and Chalk Marl. The Upper and Medial Chalk he stated 

 to comprise the chnlk with flints (the upper division of other geologists), 

 and the au(li>'r consiidcr? this distinction legitimate, inasmuch as the 

 u])ponuost brd ;it X<M-\\i('h contains organic forms which are not met with 

 in the nu-dial hc(\. Tlie distinguishing characteristics of the several 

 l)rds \\\[\\ their ]ivH'uliar fossils, and the local limits of each formation were 

 fully di'scribod, and the paper was illustrated by an elaborate section of 

 the strata of the county. 



^ 2. "On the Plasticity and Odour of Clay." By C. Toralinson, Esq. 

 The author pointed out some of the most remarkable considerations in re- 

 lation to this subject, sucli for instance as the fact that clay is only plastic 

 \\y to n certain tempera inrc : when heated beyond that point (which the 

 author believes, from experiments performed by him, to be somewhere be- 



