556 MB. H. H. AKNOLD-BEMROBE ON THE [-'^^g- 1 899, 



Appendix on the Petrography of the Rocks of Congleton Edge. 

 By H. H. Arnold-Eemrose. 



1. The Agglomerate in the Quarry. 



The following specimens from the agglomerate in the quarry were 

 collected by the writer and examined microscopically : — Two of hard 

 and three of softer agglomerate, one block of yesicular rock, and two 

 blocks of limestone embedded in the agglomerate. 



A hard agglomerate (978)^ consists of lapilli of irregular 

 shape, set iu a brown matrix, containing a few minute lapilli and 

 probably Monticulipora. The lapilli are very rarely vesicular, and 

 then only contain few vesicles. The fragments with few or no 

 vesicles contain altered felspar-laths and olivine in a dark base, 

 which is almost isotropic. The lapilli are often surrounded by a 

 vein-like fibrous calcite. 



In another specimen of hard agglomerate (979) the lapilli are 

 in a remarkably fresh state of preservation. They contain olivine- 

 phenocrysts altered to calcite and sometimes to serpentine, with 

 augite and felspar in a yellow isotropic base. The augite is 

 fresh, and occurs in idiomorphic crystals and prisms, often arranged 

 in groups or clusters. The felspars are fresh and clear, and have 

 a sharply-defined outline. A few small vesicular and non-crystalline 

 lapilli are present. The lapilli are cemented together by a limestone- 

 paste, in which occur foraminifera and other organisms, together 

 with a few fragments of augite and felspar and a subangular quartz- 

 grain. The rock may be described as a basalt- tuff. 



A piece of the softer agglomerate (981) consists of fragments 

 of doleritein a limestone-paste, containing veins of calcite and traces 

 of organisms. The igneous fragments consist of pseudomorphs of 

 felspar and olivine in a reddish matrix, which is in most cases free 

 from vesicles. A few small vesicular lapilli without crystals are 

 present, and have in many cases undergone alteration. 



A second specimen of the softer agglomerate (982) contains 

 vesicular and non-crystalline lapilli altered to calcite. Other lapilli 

 consist of altered felspar-laths with ragged ends and pseudomorphs 

 of olivine, in a red (sometimes almost black) matrix. The long axes 

 of the felspars are generally parallel one to another. A small 

 quantity of unaltered augite is probably present in one lapillus. The 

 cementing-material contains Monticulipora. 



A third specimen (983) consists of lapilli in a cement of smaller 

 volcanic detritus. The larger fragments consist of pseudomorphs 

 of olivine and felspar-microliths, sometimes in a dark red, and at 

 other times in a lighter, isotropic matrix with oxide of iron. The 

 smaller lapilli are vesicular and contain no crystals. 



A vesicular block from the agglomerate (980) is a much- 

 altered rock, consisting of pseudomorphs of olivine and felspar, 



^ The numbers in parentheses are those of the slides in the writer's 

 collection. 



