106 REPORT 1871. 



FurtJier Experiments and Remarks on Contortion of Bochs. 

 By L. C. MiAiL. 

 After recapitulating the results of some experiments on contortion of mountain 

 limestone brought before the Association at Exeter, the author went on to state that 

 ■with improved apparatus he had extended his experiments to various substances. 

 Limestone appeared to be exceedingly plastic when long subjected to forces of low 

 intensity. Flagstones fi-om the Coal-measures with a certain amount of elasticity 

 possessed little power of permanent deflection. This negative result is, however, 

 to be checked by observation of cases of accidental flexm-e of flagstones. Examples 

 were cited of these rocks which had yielded to strains, and had become perma- 

 nently bent. Plaster of Paris the author finds remarkably plastic, and a long 

 series of experiments with dry slabs shows that it can be bent and twisted inde- 

 finitely. Slates had also been tested, but with quite inconspicuous results. A 

 considerable elasticitjr was found to characterize good slate, -with a quite inappre- 

 ciable plasticity. The author had obtained striking examples of artificial contor- 

 tion by imbedding laminse of various rocks in pitch. These residts were applied 

 to the very sharp flexures sometimes seen in hard strata lying in beds of shale. 

 Cases of quite superficial contortion were quoted, and from numerous instances 

 of marked undulations in sti-ata which were underlain by horizontal and undis- 

 tm-bed layers, it was inferred that many contortions extend only to trifling depths. 

 A case of contortion traceable to the removal of part of a hill-side by a landslip 

 was referred to as showing that flexures on a considerable scale may be of quite 

 recent origin. In conclusion, some remarks were made on the general theory of 

 contoi-tious at the surface of the earth. 



On the so-called Hyoid plate of the Asterolcpis of the Old Bed Sandstone. 



By j0H3f MiLLEK, F.G.S. 



In the Number of the ' Geological Jom-nal ' for August 1869, the author pub- 

 lished a letter, stating that he had obtained two specimens of the Aderolepis from 

 the great flag-deposits of Caithness, which showed clearly and distinctly that what 

 had hitherto been considered to be the hyoid plate was not a hyoid plate at all, but 

 was in reaUty the dorsal plate of the Asterolejns, fitting on immediately behind the 

 cranial buckler, pretty much in the same way as the dorsal plate of the Cuccostciis 

 fitted on behind its 'head-plates. He stated tliat he would endeavour to lay his 

 specimens before the Geological Society of London as soon as possible ; however, 

 circumstances have prevented this. The specimens referred to were exhibited 

 on the present occasion, in fulfilment of the pledge given to the Geological 

 Societ)'. 



It is right to premise that from the time these plates were first made known to 

 geologists by Asmus and Eichwald in Eussia, and by Sir Eoderick Murchison and 

 Agassiz in the west of Europe, they have been regarded in Russia and in this 

 country as hyoid plates, down to the period of the publication by Pander of his 

 works on the Devonian sj'stem of llussia, in which he stated his opinion that they 

 would turn out to be dorsal plates when more complete fossils turned up. This 

 opinion was shared in by several of our most eminent palaeontologists, and amongst 

 others by INIi'. Peach, who has long worked in the Asfrolepts-heis of Caithness, and 

 is well acquainted with the geology of that county. 



Li his description of the Asterulepis, Hugh Miller says (' Footprints of the 

 Creator,' p. 85 of the edition of 1861) : — " That space comprised -within the arch of 

 the lower jaws, in which the hyoid-bone and branchiostegous rays of the osseous 

 fishes occur, was filled by a single plate of great size and strength, and of singular 

 form" O'iirf. fig. 40). 



And again, at p. 87 (Jhid.) : — " The two angular terminations of the hyoidal 

 plate [a, a, fig. 40) were received, laterally and posteriorly, into angular gr-ooves in 

 a massive bone of very peculiar sha|5e (fig. 42), of which the tubercled portion (a, a) 

 seems to have swept forwards in the line of the lower jaw." In the.se short 

 exti-acts Hugh MUler, -with his characteristic unmistakable clearness, states the 

 generally received opinion regarding the position of the so-called hyoid plate ; and 



