xliv PEOCEEDryGS OF THE 



gTPiitcr number of tlicm having; a large block of stone upon the top. The 

 question as to the manner in -which they were formed had already been solved by 

 o-eologists, but its solution might probably be unknowii to many of the members 

 of the Society. 



The valley in -which the pyramids stand is an old valley, probably excavated by 

 a glacier at a time when the temperature of that part of Europe was somewhat 

 odder than it now is, and was partly filled n-ith a thick deposit of moraine 

 matter, consisting in the main of a micaceous sand with a small amount of clay 

 intermixed, derived from the grinding away of red porphyry and granite, with 

 pebbles and large blocks of which, the sand was interspersed. 



The stream which now runs along the bottom of the valley must, when the 

 glacier first reti-eated and left the moraine matter, have flowed at a much higher 

 level. As it worked its way down through the hard sand, side streams would 

 run in during the heavy rains, which are not unfrequent. The course of these 

 would be guided partly by cracks formed dui'ing the heat of summer, and partly 

 by certain portions of the sand being protected from the action of the rain by 

 the large blocks of stone lying on the surface, or laid bare by the sand above 

 them having been washed away. These side streams in course of time formed 

 deep lateral ravines opening into the main valley ; but as the ridges between 

 each of these lateral ravines were only in places protected from the effects of 

 the rain by the large blocks of stone, they also got cut into so as to form a 

 second series of lateral ravines opening into the first, and thus these irregular 

 lines of columns were left. 



Although the stones, which acted like umbrellas for the columns, preserved 

 them for a long time, so long indeed that the columns might gradually be de- 

 veloped so as to become fifty or sixty feet high, yet eventually the power of the 

 -weather was too great for them, and their supports were weakened so that they 

 fell. The columns having lost their covering, gradually became pointed like 

 church spires, but eventually were -n^^shed away, as the bottom of the valley to 

 the height of 100 or 200 feet above the stream was now free from columns, which 

 now are only found higher up the slope. 



The essentials for the formation of such columns, which have been noticed in 

 several parts of the world, seem to be 



1. A soil readily acted on by water, but sufficiently hard and compact to 

 carry a great weiglit, and through which a valley has been cut. 



2. An admixture in the soil of large blocks to protect it from the rain in 

 certain places only. 



3. Occasional rains sufficient to cut deep gullies. 



4. A main torrent at the bottom of the valley capable of removing all the 

 sand and blocks washed into it, and of keeping the sides of the valley in which 

 it runs inclined at a high angle. 



4. "On the Supposed Recent Extinction of Cyclosfoma eleqans 

 in North Herts." By H. George Fordham, F.G.S. ( Vide p. 172). 



5. " On the Anacharis /jlsinai^trum in the River Colne, near 

 Watford." By Alfred T. Brett, ^I.D. ( Vide p. 17.3). 



6. A letter from ^\r. 11. A. Pryor, ]?.A., 1\L S , giving a list of 

 plants he has recently discovered in new stations in the neigh- 

 bourhood of Watford, and notes on the blossoming of certain 

 spring wild-flowers during the last fe-n' -weeks ( Vide p. 173). 



7. A hitter from ^l\\ ('laronce E. Fry on the recent capture of 

 the oleander hawk-moth ( Chwrocampa Nerii) at Hemcl Hempstead 

 {Vide^. 174). 



The Secretary recorded the discovery, near St. Albans, by Miss 

 Willshin, of Campanula lafifolia, a species of which the only 

 previous record of the occurrence near St. Albans, many years ago, 

 by Miss HeiLslow, liad been considered doubtful ; and of a new 

 thistle which Mr. Pryor considered to be a hybrid between Carduuft 



