30 
PRE-CAMBRIAN VOLCANOES 
BOOK II 
strcata of Caradoc or Bala age ; that by a great hiatus in the stratigraphy 
the Upper Silurian series transgressively wrapped round everything below it; 
that yet again the Coal-measures crept over all these various I’aheozoic lornia- 
tions, followed once more unconformably by Permian and Triassic deposits.^ 
Besides all this evidence of extraordinary and repeated terrestrial move- 
ment, it was found that the region was traversed by some of the most 
powerful dislocations in this country, while to complete the picture of 
disturbance, many protrusions of igneous rocks were recognized. 
In a territory so complicated, though it had been sedulously and 
skilfully explored, there could hardly fail to remain features of structure 
which had escaped the notice of the first observers. In particular, the 
igneous rocks had been dealt with only in a general way, and they 
consequently offered a favourable field for more detailed study ; while by a 
more searching examination of some of the rocks for fossils, important 
corrections of the earlier work might yet be made. 
A notable stop towards a revision of the received opinions regarding the 
igneous rocks of this region was taken by Mr. Allport, who showed that the 
so-called “ greenstone ” included masses of devitrified spherulitic pitchstones 
and perlites, together with indicated volcanic breccias, agglomerates and 
ashes.^ Bubseciuently Professor Bonney described more fully the petro- 
graphical characters of the Wrekin igneous rocks, confirming and extending 
the observations of Mr. Allport.* 
But the correction of the prevalent error as to the geological age of 
these rocks was due to Dr. Callaway, who, after spending much time and 
labour in ascertaining, by a careful search for fossils, the position of the 
superincumbent rocks (wherein he discovered Cambrian organisms), and in 
a detailed investigation of the structure and relationships of the igneous 
masses themselves, was led to regard them as part of an ancient pre- 
Cambrian ridge ; and he proposed for the volcanic group the name of 
Uriconian, from the name of the former Roman town which stood not iar 
to the west of them.^ He has shown how essentially volcanic this ancient 
series of rocks is, how seldom they present any clearly -marked evidence of 
stratification, and how small is the proportion of sedimentary material 
associated with them.’’ 
Sulisequently Professor Lapworth, by his discovery of the Olenellus- 
fauna, marking the lowest known fossiliferous Cambrian zone in the Wrekin 
1 The area is embraced iii Sheet 61 of the Geological Survey, and is illustrated by No.s. 33 and 
36 of the .sheets of Horizontal Sections. In the early editions ot tlie Survey maps the ‘ ‘ felspathic 
traps” and the “greenstones” of the Wrekin district were distinguished by separate colours, 
but unfortunately this useful and so far correct discrimination was given up in subsequent 
editions, where all the acid and basic rocks are merged into one. 
- Quart. Jo'urn. Gaol, Soe. vol. .vxxiii. (1877) p. 449. 
® Op. cit. vol. XXXV. (1879) )i. 662 ; vol. xxxviii. (1882) p. 124. 
j Quart. Journ. Gcol. Sue. vols. xxx. (1874) p. 196, xxxiv. (1878) p. 754, xxxv. (1879) p. 643, 
xlii. (1886) p. 481. For a criticism of Dr. Callaway’s views as to the order ol succession among 
the rocks of this district, see Prof. Blake, up. cit. vol. xlvi. (1890) p. 386, and Dr. Callaway s reply, 
vol. xlvii. (1891) p. 109. 
^ Op. cit. vol. .xlvii. (1891) p. 123. 
