488 



THE GEOLCGIST. 



]VIr. Mackeson, of Hythe, acted as the scientific teacher of the party throughout 

 the excursion. 



On arriving at the brovr of the Undercliff, near No. 3 Martello Tower, he com- 

 menced his address by esplaiuing vrhat was meant by the Cretaceous Formation, 

 viz. : — A series of beds distinguished by very distinct lithohtgical characters, but 

 forming a natural group when considered with reference to their fossil organic 

 remains. This formation is sub-divided by geologists into, 



1. The Chalk; 



2. The Upper Greensand ; 



3. The Gault ; 



4. The Lower Greensand ; 



as was illustrated by a diagram, representing the section from Folkestone 

 Hill to Copt Point, displaying this order and superposition of the beds. 



The Upper Gre:n;o.n I. here very feebly represented, was first examined. In a 

 wester]-- : - - ~ : "n. in Surrey, and in the Isle of Wight, it forms a 

 bed 01 _ ::aining numerous fossils; but here it appeared 



to have -Ul ....i.... \ thickness probably not exceeding three or four 



feet, and its fossils I'eiug levr aud far becvreen. 



Descending to Cc^p: Point, that unrivalled section of the Gault with its 

 numerous int-ro-rnj losslls. vras Jilated upon ; particular attention being drawn 

 to the state in vrhi hi the ;h'^?ll< oi Ammonites, Ilamiics, Inocerami, &c., are there 

 preserved. The estimated thickness of the Gault is about 120 or 130 feet. 



Taking up a position on the out- crop of the Lower Greensand, Mr. Mackeson 

 explained to the members that the history of this interesting group of sands and 

 clays could not be fully enterol upon, inasmuch as only the uppermost of its four 

 subdivisions offered itself to their notice within the range of the day's 

 excursion. Examples of false stratification were exiDlained, and the innu- 

 merable traces of large sponges on the rock-masses pointed out. The pro- 

 minence of the Copt Point was due to the resistance of the Greensand Ptocks 

 to the aciion of the waves. The junction of the Lower Greensand and Gault, 

 there visible, proved the beds to be conformable, and was the subject of numerous 

 remarks, and the profusion of coniferous wood thereabouts, often bored by 

 Teredos, was adduced to prove the existence of contemporaneous pine-forests, 

 which must have grown on land then above the level of the ocean. 



The phosphate of lime-nodules abounding in this junction-bed are by the aid of 

 the chemist's ••magic art,'' valuable to the agriculturist, after manufactureinto 

 stiper-phosphate of lime. 



The existence of these nodules here was first remarked many years ago by that 

 veteran geologist, Dr. Futon ; and in a lecture at Folkestone, in 1817, their abund- 

 ance and mercantile and agricultural value was pointed out by the present editor 

 of the GEOLOGisr. 



Passing along the shore in the direction of Dover, the lecturer di*ew the 

 attention of the members to a conglomerate of shingle and lime, concreted by the 

 springs flowing from the chalk, holding carbonate of lime in solution. The 

 universal use of artificial couerece at the present day gave an additional interest 

 to this — Nature's ovrn work — in which the matrix of lime was scarcely less 

 indurated than the included pebbles of fiint. 



A halt was called near the Pelter coast-guard station, where the lectni'er ex- 

 plained how the beautiful undercliff extending under the white and beetling 

 cbalk-clifls from Copt Point to this spot was due to the waste of the lower and 

 softer beds by the sea, and the consenuent downfall of the harder superincumbent 

 chalk-strata. 



Mr. Mackeson here threw a hasty glance at the geology of the Bas Boulonais as 

 intimately connected with that of the south-east of England, and alluded to the 

 occurrence of the true Coal-measures at Hardinghen, near Boulogne, the possible 

 continuation of which across the Channel was pointed out shortly since by Mr. R. A, 

 Godwin-Austen in a most valuable paper before the Geological Society, London, and 

 which proved the possible occurrence of coal at no vast depth within the area, 



