Quartzose Conglomerate at Caldon Loiu, Sto.fordsJtire. 79 



On comparing the above with the list given by Messrs. Jackson 

 and Alkins, it will be noted that the fauna of the conglomerate 

 is quite a different one, and is indicative of a much higher horizon. 

 Beete Jukes was evidently correct when, in 1839, in a section across 

 North Staffordshire in his paper, '' Sketch of the Geology of Derby- 

 shire,"^ he shows the beds at the base of Caldon Low to be fairly 

 low down in the series. 



Petrography of the Conglomerate. — The pebbles in the con- 

 glomerate vary greatly in size and in number, and comprise many 

 rock types. The largest are the angular and subangular blocks of 

 grey Caldon Low limestone, while smaller but rounded fragments 

 of the same material are common. In general the material of finer 

 grain is decidedly water- rolled. So far as distribution is concerned, 

 the marginal portions of the conglomerate are much less rich in 

 pebbles than the interior, but even in the latter the proportion 

 of visible detrital material varies from place to place. In addition 

 to the rock containing large limestone fragments, several distinct 

 types of conglomerate can be distinguished ; first, a rock containing 

 numerous pebbles, up to an inch or two in diameter, with relatively 

 little matrix ; secondly, a similar but more fine-grained rock ; and 

 thirdly, a very fine-grained limestone, with abundant minute 

 fragments of quartzose material. The pebbles include fragments 

 of grey Caldon Low limestone, fossiliferous limestone, several 

 types of quartz rocks, cherts, shales, T^ydian stone, and some altered 

 igneous material. 



Several specimens of the conglomerate and the normal Caldon 

 limestones have been sectioned and examined microscopically. 

 The ordinary Caldon Low limestone shows no trace of quartzose 

 material, and is composed mainly of organic remains, including 

 brachiopod shells, crinoid stems, fragments of corals, tests of 

 foraminifera, etc., in a matrix which is ap^^arently structureless, 

 and was probably a calcareous mud originally. Crystalline calcite, 

 apart from veins and joints, is conspicuously absent. The larger 

 fragments of limestone in the conglomerate are very similar. 



The coarse quartzose conglomerate consists of several types of 

 rocks and organic fragments cemented together by relatively large 

 crystals of calcite. The shells and other calcareous materials are 

 obviously fragmental, and the lack of internal structure and optical 

 homogeneity of many fragments suggest that recrystallization has 

 occurred. Often the calcite of the matrix has crystallized round 

 the detrital Hmestone in such a way as to be optically continuous 

 with it. Pieces of dolomitized material and oolitic grains can also 

 be seen. 



Several types of quartz-rock are present. Vein-quartz occurs 



commonly, each piece being optically homogeneous except for the 



presence of strain shadows, which are sometimes so prominent 



and so orientated as to indicate that the material has undergone 



' Analyst, vol. ix, 1839, p. 2. 



