264 ME. H. H. AKNOLD-BEMKOSE ON [^-Ug. I9O7, 



sufficient to distinguish it from a bedded tuff. Sir Archibald Geikie 

 expresses the opinion that it ' probably belongs to another vent/ 

 and states that 



' it is particularly interesting from the great preponderance of limestone-frag- 

 ments in it.' (' Ancient Volcanoes of Great Britain ' vol. ii, 1897, pp. 17-18.) 



The rock consists of a calcareo-igneous breccia, and is a mixture 

 of limestone-fragments containing fossils (some angular, others more 

 or less rounded), and of volcanic lapilli and detritus which are often 

 of a dirty-green or red colour. The proportions of calcareous and 

 igneous material vary considerably. In some parts the rock con- 

 sists of fragments of limestone, with little volcanic detritus ; while 

 in others it is composed of softer and more comminuted materia 1 

 enclosing rounded fragments of limestone. 1 



An interesting specimen obtained from a wall in Ember Lane, and 

 shown to me by Mr. W. J. P. Burton, contained a small fragment 

 of wood. Dr. G. T. Prior, of the Natural History Museum, kindly 

 lent me a thin slice of the rock. A photomicrograph magnified 50 

 diameters was made by me and submitted to Prof. A. C. Seward, who 

 pronounced it to be wood ; but, in the absence of a longitudinal 

 section, he could not determine its nature. This is, so far as I am 

 aware, the only particle of wood that has yet been found in the 

 fragmental igneous rocks of Derbyshire. 



Moor-Lane Vent. — In Moor Lane, about 160 yards west of the 

 Bonsall sill, a small patch of agglomerate is seen in the banks of 

 the lane. It consists of lapilli and small pebbles of fossiliferous 

 limestone cemented by a calcareous paste. The bigger lapilli contain 

 felspar-laths. It is uncertain whether this rock represents a bedded 

 tuff or a vent. But, from the fact that it cuts across the strike of the 

 limestones to the south-west, I have ventured to map it as a small 

 vent. 



Hop ton Vent. — About 2 miles south-west of Wirksworth, and 

 a short distance east of the village of Carsington, is the southernmost 

 vent of the Matlock district. It is elliptical in area, the major axis 

 measuring about a third of a mile in length and extending in a 

 north-westerly direction, and the minor axis about a furlong in 

 length. A short distance to the east of the agglomerate the 

 limestones are seen dipping 10° to 20° south-eastward. Immediately 

 north of the igneous rock the dolomitized limestones dip south- 

 eastward ; but, as the hill towards the Via Gellia is ascended, the dip 

 is seen to decrease, and near the High-Peak Railway the beds are 

 horizontal. This outcrop of toadstone was mapped by the Geological 

 Survey as interbedded with limestone, and was supposed to be over 

 1000 feet down in the series and below the toadstone (lower lava 

 of Matlock) seen in the cutting of the High-Peak Railway. 2 

 Sir Archibald Geikie considered the agglomerate to form a true vent 



1 Quart. Journ. Geol. Soc. vol. 1 (1894) pp. 632-33. 



2 Geol. Surv. Mem. « North Derbyshire V 2nd ed. (1887) p. 24. 



