270 Mr. H. C. Goodman's notes on the 



One thing is quite certain, that the flies are parasitic upon the 

 bees ; and it is remarkable that they should, undetected, obtain 

 admission into their nests, when it is well known that so many 

 Hymenoptera detect not only intruders of other species, but even 

 of their own species of another colony, and ruthlessly expel them. 



At the same time it is well to remark that there are several 

 genera of "Cuckoo-bees," which are parasites in the nests of 

 other bees, feeding on the food stored up by their industrious 

 hosts ; and the species above mentioned, Bombm lapidaritis, hag 

 a red-tailed cuckoo-bee parasitic upon it. 



86. — Notes on the Geology of the Isle of Purbeok. 

 By C. H. Goodman. 

 (Read Sept. 10th, 1890.) 



That part of Dorsetshire lying S. of the River Frome and 

 Poole Harbour, and known as the Isle of Purbeck, is about 

 14 miles long by 7 wide, and presents many features of geological 

 interest. The most conspicuous is a great central chalk range 

 running E. and W., on one point of which Corfe Castle stands. 

 On the north side extends the low-lying Bagshot sands, and 

 here is preserved an interesting local object. Situated on a low 

 hill, and conspicuous on the moorland, is the " Agglestone," 

 computed to weigh 400 tons. It is a hard concretionary block, 

 left after the denudation of the surrounding soil. 



Passing now by steamer round the eastern extremity of the 

 chalk range referred to, deep indentations in the coast can be 

 traced, also stacks already isolated by the sea, and others in 

 the process of formation, -The strata are horizontal, but near 

 the southern side exhibit a most striking contortion, being 

 suddenly bent up to a vertical position. The recess beyond 

 forms Swanage Bay, composed mainly of the Wealden clays 

 and Hastings sands. Lyall says it cannot be less than 2000 

 feet thick ; it is productive of reptilian remains, and the usual 

 bands of lignite. A small stream flows into the bay through the 

 town ; and it may be worth recording that I here found Gyrinus 

 unnator, hitherto unknown on the south coast. 



Parallel with the chalk, and forming the southern boundary of 

 the valley, is the ridge from which the island takes its name, and 

 which gradually dips eastward, terminating in the projecting 

 rocks, called Peveril Point. The beds are divided into upper, 

 middle, and lower Purbeck. The upper produces the well-known 

 Purbeck marble, a fresh-water limestone containing Paludina, 



