120 DKEDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



and the microscope invaluable, since much of the minuter evidence 

 afforded by a rock is as direct and positive as that on a large scale. 

 It has been impossible to microscopically examine every variety found, 

 but one hundred sections in all have been prepared, and it is hoped 

 that most of the rocks may safely be grouped around those thus 

 represented. 



Before entering upon detail, it may be well to pass in review the 

 manner in which the problem has been attacked by the various 

 investigators. Austen used both sounding-lead and dredge, he differ- 

 entiated the textures of the deposits, giving such statements as that 

 the gravel was of the size of almonds, beans, olives, walnuts, or the 

 ground was stony, or large angular and rounded blocks occurred ; he 

 mentions flint, granite, black granite, tin-stone, serpentine, etc., but 

 with no clearer lithological definition, and he records any shells of 

 littoral species found in the deeps. His observations covered the 

 whole Channel bed, but not closely, and extended from the Nymph 

 Bank to near Dover. 



Delesse, with greater attempt at detailed location, but with less 

 information as to the size of the constituents of gravels, maps out the 

 Channel, discriminating between areas covered by ' argile,' ' craie,* 

 * sable/ ' sable riche en coquilles,' ' sable sur les roches pierreuses,' 

 ' roches pierreuses,' * roches en pierres dfeagregees,' and ' roches en 

 pierres pourries ou decomposees.' He trusted to the sounding-lead for 

 his samples, and none is recorded as coarser than gravel, while none 

 which came from a greater depth than 28 metres is lithologically 

 examined in detail ; most were obtained very near the French coast. 



Hunt chiefly derived his material from the occasional boulders 

 captured in fishermen's trawls off the south coast of Devon ; the 

 more part of these were decidedly heavy, ranging from about 3 to 

 about 12 cwt. All were examined microscopically by modern methods. 



R N. WoKTH was supplied with blocks and stones of some size 

 which had become entangled in long lines or bolters ; he, too, examined 

 the rocks microscopically. 



The Association has conducted systematic dredgings and endeavoured 

 to obtain fair samples of the bottom-deposits, including sands, gravels, 

 pebbles, and small boulders. Its gear has not permitted the capture 

 of the larger blocks which undoubtedly occur, but three of these have 

 been traced which have been obtained by fishermen, and hand speci- 

 mens taken. Where pebbles have been dredged, in the later work at 

 least, these have been entirely depended on for information as to the 

 lithology of the station ; in the earlier work, where pebbles were 

 scarce, the sand was examined in detail also. The superior facilities 



