394 MR. A. V. JENNINGS ON THE [^^g* 1 899, 



It seems impossible that these ' mixed ' schists should represent 

 a geological formation referable to some particular horizon. Bearing 

 in mind that the Arosa variolites occur similarly in combination 

 with red and calcareous bands, and that (as Prof. Steinmaun has 

 shown) even more typical ' Griine Schiefer' may exhibit a sphe- 

 roidal structure on weathered surfaces, it seems probable that the 

 rocks owe their character to local conditions and are connected with 

 the intrusion of the ' ophiolitic rocks.' 



(iii) The Ophicalcareous Grits. 



I suggest this name for some peculiar rocks which occur only, so 

 far as I know, in the neighbourhood of the Todtalp and the Parsenn- 

 Purka Pass. The ' red calcareous rock ' referred to by Dr. Ball is an 

 example, but other varieties may be coarser grained, dark blackish- 

 green in colour, and with grey argillaceous films. 



It is dijfficult to find these rocks in position, but it will be noted that 

 their area of occurrence is precisely where the field-evidence indicates 

 the local overthrusting referred to on p. 392. I have not found 

 them east or west of the upper Todtalp, and they do not seem to follow 

 the strike of the strata for any appreciable distance. 



They are of a fine or coarse granular structure, and closer obser- 

 vation proves that their chief constituents are calcite and serpentine. 

 Considering the position in which they are found, it therefore seems 

 probable that they are ' crush-grits ' of serpentine and limestone.^ 



Prof. Bonney, who has kindly given much attention to these and 

 other rocks that I have collected, suggests the possibility of such a 

 rock being produced by the washing down of serpentine-grains from 

 a pre-existent shore. This seems quite possible in theory, but I 

 believe it has not yet been proved to occur elsewhere. If such a 

 process had occurred here we should expect to find the same rocks 

 elsewhere along the strike of the stratified rocks ; their extreme 

 localization seems to favour the ' crush-grit ' hypothesis. 



(iv) The Eadiolarian Hornstones. 



Along the crest of the Cotschna ridge runs a contorted band of 

 red rocks, composed of cherts or ' hornstones ' passing into red 

 shales. In thin sections the cherts are found to be crowded with 

 radiolaria, and are doubtless the same as those found by Steinmann 

 at Arosa, and regarded by him as of Jurassic or later age. In this 

 locality I do not see how that opinion could be maintained. 



From the radiolaria themselves one can scarcely expect con- 

 clusive evidence, since our knowledge of characteristic Triassic forms 

 is practically nil. Dr. G. J. Hinde has been kind enough to 

 examine the microscopic sections, and, though the condition of pre- 

 servation is not satisfactory, he is able to recognize some 15 generic 



^ It seems to me probable that some rock of this kind may have given rise 

 to Theobald's statement as to the transition of the Lower Eauchwacke into 

 Yerrucano. See p. 389. 



