466 Revievjs — Penning' s Field Geology. 



from the top of a coach, were at the time sufficiently accurate for 

 the scale of map he used, and considering the amount of country he 

 personally examined, his work could not be surpassed by any one 

 man. Even the early maps of De la Beche, grand works as they 

 will always remain, necessarily lack the minute precision that the 

 labour of many lives alone could give it ; for the detailed mapping 

 of the whole of Devon and Cornwall would probably occupy more 

 than the entire lifetime of the most expert Geologist. 



The old work, carried on for the most part by noting carefully all 

 the junctions between two formations observed in travelling along 

 the roads, and then carrying on the boundary-line according to 

 contour or the hill-shading on the map, must now be supplemented 

 by careful attention to minor features, if any advance is to be made 

 in Field Geology. And it is only by such careful attention to detail 

 that the structure of a country can be rightly understood, or a correct 

 inter^Dretation be made of the varied forces which have combined to 

 sculpture its scenery. To carry on a minute survey of a country 

 one must be prepared to staj'- many weeks or months at one locality, 

 and in an entirely fresh district it will take at least a month of hard 

 work to get well acquainted with the character and mode of occur- 

 rence of the rocks, before any regular mapping is commenced. How 

 to set to work is to the novice a matter of considerable difficulty. 

 The advantages enjoyed by those who serve on H. M. Geological 

 Survey are great, inasmuch as the beginner can start at once under the 

 guidance of some trained man. But those who would wish to start 

 independently, and work out the geology of a district for themselves, 

 have had no guide and philosopher to direct their footsteps, if we 

 except some scattered notes in geological text-books, and the brief 

 hints given by Jukes in his " Manual," and by Clifton Ward in his 

 " Elementary Geology." Mr. Penning, an experienced Government 

 Geologist, now steps forward and presents us with a concise hand- 

 book of Field Geology, to which his colleague, Mr. Jukes-Browne, 

 has contributed some notes about the use and abuse of fossils. The 

 work commences with a description of maps, and of the instruments 

 necessary for geological work. The author then takes us out into 

 the field into a country of Eeading Beds, Chalk, Greensand, Gault, 

 and Alluvial deposits, where perhaps the simplest kind of field-work 

 can be met with. He explains very clearly the character of the 

 work and the method of proceeding, and so far we feel we could 

 get on very comfortably. In a subsequent chapter he takes us on a 

 survey of the older rocks, the Trias, Permian, and Carboniferous 

 rocks, and a felstone dyke, and the work again seems so clear and 

 straightforward that we regret he does not take us a step further, 

 and illustrate the mapping of a more complicated district where the 

 rocks are greatly contorted, where the stratification is obscured by 

 cleavage, and where there are striking instances of unconformability. 

 The discrimination between faults and unconformabilities, and, in 

 the case of eruptive rocks, the determination of those which are 

 intrusive and those which are interbedded and conformable, require 

 more notice than the author has given to them, as likewise do the 



