338 MICEOSCOPIC MATEEIAL OF [vol. Ixxiii, 



the localities collected from, could be described as Upper Mottled 

 Sandstone. 



The speaker was interested to find that a belt, containing a high 

 proportion of heavy minerals, extended across the strike of the 

 Eunter opposite Gorsethorpe. This was confirmation of his ex- 

 planation given some years ago of the origin of the Mansfield 

 Sandstone in the so-called ' Permian ' below. The explanation 

 required a river flowing in from the Pennines, in practically the 

 position described by the Author. 



The Author was to be congratulated on the work that he had 

 done. It had been customary for geologists to collect Eunter 

 pebbles, and ignore the sands in Avhich they hj. Dr. Thomas had 

 done pioneering work in Devon on these sands, and the Author had 

 now accompHshed useful work in another area. 



Dr. P. Gr. H. Eo SWELL remarked that a paper dealing with the 

 petrography of the Eunter deposits Avas certain to be of consider- 

 able interest, and the Author's contribution was clearly no 

 exception to the rule. While the records of detrital -mineral 

 assemblages were very valuable, it was obvious that great caution 

 should be exercised in drawing inferences regarding the source 

 of the material. A great deal rested on the number of samples 

 collected, their selection, and their vertical and lateral distribution. 

 With regard to this, he (the speaker) wished to utter two words of 

 warning, which might, however, be unnecessary in the case of the 

 paper under discussion. 



The variation in the percentage weight of the heav}^ mineral 

 residue did not necessarily give any indication of the source of the 

 material. It was now an established fact that the heavy crop 

 increased with the decrease in grade-size in sands, and the grade 

 or mixture of grades in every sample must therefore be determined. 



In the next place, the presence of minerals of metamorphic 

 origin, such as tommaline, staurolite, garnets, micas, etc., in sedi- 

 ments did not necessarily indicate origin from metamorphic rocks. 

 Such minerals were frequently the least unstable, and were foimd 

 in most sedimentary rocks in the British area : some of them 

 might have passed through several geological cycles, and have been 

 derived direct!}^ from older sediments. 



Mr. Eeenaed Smith was of o23inion that the chief value of 

 the Author's work consisted in his careful and useful determination 

 of the mineral residues, but that much more work of a similar 

 nature must be undertaken before such broad conclusions could be 

 drawn Avith safety. He emphasized the fact, which he himself had 

 been the first to put on record, that at Farnsfield the direction of 

 dip of the cross-bedding was roughh^ from south to north, sAvinging 

 now to the Avest and noAv to the east. While agreeing in general 

 with the objections raised b}^ Dr. Sherlock, the speaker Avas not 

 prepared to folloAv him' in suggesting that the Pebble-Eeds were 

 accumulated by river-action on an exposed coastal shelf, but con- 

 sidered that they were deposited in shalloAv water. The pebbles 

 appear to have entered the district from the south, but probably 



