86 Reviews — Dr. A. R. Dwerryhouse — Geological Maps. 



will find in the beautiful text-figure restorations much important 

 material for generalizations. The actual fossils are represented on the 

 plates by a series of photographs. 



A. S. W. 



II. — Geological and Topographical Maps : their Interpretation 

 AND Use. By Arthur 11. Dwerryhouse, D.fSc, F.G.S., Lecturer 

 in Geology in the Queen's University of Belfast. 8vo ; pp. vii, 

 133, with 90 text-illustrations. London: Edward Arnold, 1911. 

 Price 4s. &d. net. 



THIS work, intended as "A Handbook for the Geologist and Civil 

 Engineer ", is clear and concise, and illustrated (as the author 

 tells us) mostly from actual districts in the British Isles, although 

 the localities ai'e only given in a few instances. 



Commencing with a description of topographic maps, of the different 

 scales adopted by the Ordnance Survey, and the methods of depicting 

 the physical features, the author proceeds to give examples of the 

 construction of sections from contoured maps, with a reminder that 

 the miles represented along a road in a hilly country are longer than 

 those on flat ground. The methods of constructing maps in lands 

 where none exist are not dealt with, but the author gives instructions 

 for rough surveys of small areas by means of the prismatic compass, 

 in cases where more local topographic detail is wanted. 



Turning to geological maps the various scales of those issued by tlie 

 Geological Survey of the British Isles are duly noted, as well as the 

 particular uses of the sheets issued with Diift and without Drift. 

 Botli editions, it may be remarked, are desirable in questions of water- 

 supply and tunnelling, as Drift may be 2U0 feet or more in thickness. 

 While the 6 inch maps are essential in practical inquiries, the 1 inch 

 maps are rightly regarded as the most generalh* useful ; and those 

 which in recent years liave been colour-printed have the advantage 

 in most cases of a column of formations showing their relative 

 thicknesses to scale, and of one or more longitudinal sections. The 

 process of interpreting the structure and of drawing other sections 

 is thereby greatly facilitated. For the latter purpose the 6 inch 

 maps are desirable. In other cases the student may have to draw 

 sections to ascertain the depth and thicknesses of strata from data 

 given only on the geological map itself. Here knowledge is required 

 not only of the sequence of the formations and of their thicknesses, 

 but of unconformities. Some of these may be clearly marked; others, 

 where for example Gault may rest on Oxford Clay, are only to be 

 determined after close examination of the strata and their fossils. 

 Tlie many structural features in sedimentary and igneous rocks are 

 explained and illustrated, including folds, faults, thrust - planes, 

 flaws (fractures accompanied by horizontal movements displacing 

 outcrops), and decussating folds (folded strata affected by later 

 movements). The author riglitly points out the need of paying regard 

 to the general dip as opposed to local dips in the strata when dealing 

 with the main geological features ; and he further describes 

 escarpments and dip-slopes, outliers and inliers, irregularities in 

 thickness, lenticular beds, overlap, etc. When he remarks that 



