ON THE CORRELATION AND RELATIVE AGES OF 

 THE ROCKS OF THE CHANNEL ISLANDS. 



BY MR. C. G. DE LA MARE. 



The Channel Islands, as is generally known, arc entirely 

 composed of igneous and unfossiliferous sedimentary rocks. 

 The dispersion of these islands over a wide stretch of sea, and 

 the smallness of their area are not favourable for obtaining a 

 general view of their geological structure, notwithstanding 

 that the rocks are well exposed in the coast lines and rocky 

 beaches of the various islands as well as in quarries and road 

 cuttings in the interior. Owing to these circumstances it is 

 not easy to fix the ages of the various rocks to be found in 

 these islands, and in the absence of fossils we have to trust to 

 lithological resemblances and analogies Avhich may prove 

 misleading, so that the conclusions arrived at cannot be 

 accepted as certain, and must only be looked upon as offering 

 a certain degree of probability. As might be expected from 

 the geographical position of the Channel Islands, their 

 geological structure is more intimately related to that of 

 north-western France than to that of England. It is there- 

 fore in that direction, where a large area of the more ancient 

 rocks is exposed, that we should look for the key to unlock 

 the problem involved in our rocks. But the structure of that 

 part of the Continent had not been accurately determined 

 until recently. It is therefore not to be wondered at that 

 most of the geologists who have examined and written on 

 the subject of the " Geology of the Channel Islands," have 

 contented themselves with describing the various rocks and 

 indicating their localities, and have but lightly touched on 

 their relationship to each other, or to the rocks of better 

 known districts. Of late years, however, great advances have 

 been made both in England and on the Continent in the 

 study of the more ancient rocks, and of the problems involved 

 in their intricate relations and the metamorphoses to which 

 they have been subjected. I have not had the advantage of 



