278 Reports c& Proceedings — -Geological Society of London. 



5. ROTHAMSTED EXPERIMENTAL STATION, HaRPENDEN. In llis 



Annual Report for 1912, the Director, Dr. E. J. Russell, remarks in 

 connexion with researches on soils : " Our new conception is that the 

 soil organisms may be divided roughly into two groups in their 

 relation to the processes of food production : a useful group and 

 a detrimental group. The latter are, speaking generally, more 

 readily killed than the former. Conditions that are harmful to active 

 life in the soil tend therefore to reduce their numbers, and lead to 

 an increased activity of the useful bacteria. On the other hand, 

 conditions favourable to active life tend to keep up the detrimental 

 organisms, and therefore to reduce the useful bacterial activity. We 

 have thus been able to render intelligible a number of obscure and 

 paradoxical effects that have hitherto caused considerable perplexity. 

 It has already been observed by practical men in various countries 

 that certain soil conditions harmful to the growth of organisms were 

 ultimately beneficial to productiveness : such are long continued and 

 severe frost, long drought (especially if associated with hot weather), 

 sufficient heat, treatment with appropriate dressings of lime, gas 

 lime, carbon disulphide, etc. Further, it has been observed that 

 conditions which are undoubtedly favourable to life, such as the 

 combination of warmth, moisture, and organic manures found in glass 

 houses, lead to reduced productiveness after a time." 



B.EE=OR,TS ^^IT3D I=K,OOE]EIDI3SrG-S. 



Geological Society of London. 



(i) April 9, 1913.— Dr. Aubrey Strahan, F.R.S., President, 

 in the Chair. 



The following communications were read : — 



1. " The Variation of Planorhis multiformis, lironn." By George 

 Hickling, D.Sc, F.G.S., Lecturer in Palaeontology and Demonstrator 

 in Geology in the Victoria University of Manchester. 



The writer gives an account of an investigation of the above-named 

 Miocene Gasteropod, based on a suite of 532 specimens from a single 

 block of stone. The shells of this type from the Steinheim deposits 

 were formerly investigated by Steinmann, Hilgendorf, Hyatt, and 

 others. Many species and sub-species were founded by those writers, 

 who also constructed genetic series which were described as following 

 a stratigraphical sequence. The specimens considered in the present 

 paper include several of the species and sub-species of Hyatt. Since, 

 however, these individuals were clearly all living together, and all 

 the types appeared to pass one into the other by insensible gradations, 

 it seemed doubtful whether they could properly be regarded as 

 constituting more than a single species. Accordinglj' a study was 

 made of the variation in height presented by the shells, which 

 include every gradation between perfectly discoid forms and types 

 with a spire the height of which considerably exceeds the diameter of 

 the base. By sorting the whole of the shells into ten grades, 

 according to height, it was shown that forms of mean height were 



