IV 
whom the mapping was extended into the Midland Counties. A 
little later J. W. Judd, in prolonging the work through North- 
amptonshire and Rutlandshire, introduced into it the practice of 
following out definite palfeontological zones, without which the 
systematic correlation of the fossiliferous formations cannot be 
satisfactorily undertaken. 
The northward extension of the mapping of the Jurassic for- 
mations was subsequently carried out chiefly by W. H. Holloway 
and W. A. E. Ussher, with the co-operation of W. H. Dalton, 
A. C. G. Cameron, and A. ,1. Jukes-Browne. The survey of 
these rocks north of the Humber was made mainly by C. Fox- 
Strangways, C. Reid, and G. Barrow. 
The present volume has been prepared entirely by Mr. Wood- 
ward. His training in the field-work of the Survey had made 
him intimately acquainted with the Jurassic rocks, for between 
the years 1867 and 1874 he was engaged under Mr. Bristow, 
the late Director for England and Wales, in re-surveying the 
Secondary formations in the South-west of England and the 
South of 'Wales. 
As the system of publishing sheet-memoirs in elucidation of the 
maps of the Survey did not come into operation until after 1856, 
no Memoirs have yet been issued dealing with the Secondary 
formations of Dorset, and of Western and Southern Somerset, 
excepting De la Beche's general Memoir " On the Geology of 
Cornwall, Devon, and West Somerset," which appeared in 1839, 
and his classic essay " On the Formation of the Rocks of South 
Wales .and South- Western England," which was published in the 
first volume of the Memoirs of the Geological Survey in 1846. 
Hence for a large region in the south-west of the country, em- 
bracing many of the districts where the Jurassic rocks are 
typically developed, there were no official descriptions available for 
the preparation of a general monograph. Mr. Woodward has 
thus been compelled to re-visit the ground, to study the best 
sections, and to trace the gradual stratigraphical changes of the 
several formations from district to district. The following chap- 
ters will consequently be found to contain much new material. 
All the sections, except where otherwise stated, are original, and 
the author has likewise, Avherever possible, verified the descriptions 
of other observers quoted by him. A large number of fossils 
have been collected by him, and these have been named by 
Messrs. Sharman and Newton, the Palaeontologists of the Survey. 
