SCIENTIFIC SURVEY. 267 



the soil in ledges. He supposes that if strata dip 40° north-west 

 into the ground in some prominent ledge, that the rock will con- 

 tinue to dip so two hundred feet below the surface, unless there 

 be some reason to the contrary. And if for the distance of one 

 mile, he finds four ledges of rock with equal intervals between 

 them, and all possessing the same inclination, then with reason he 

 infers that the concealed layers between the ledges have the same 

 dip. But if he finds two of these ledges to dip north-west, and 

 the other two to dip south-east towards the former, then he con- 

 cludes that the strata meet under ground and form a si/nclinal axis 

 or a sort of basin. Of if they dip away from each other, then he 

 concludes they must meet in the center, much like the roof of a 

 house, only that the top is generally rounded instead of angular, 

 and much of the crest has been worn away. Such an axis is called 

 an anticlinal axis. By such processes of reasoning is every obser- 

 vation accompanied, only the geologist does not consider it neces- 

 sary to repeat them with every measurement. He takes it for 

 granted that the reader will always supply this deficiency in his 

 own mind, if need be. 



When the geologist has travelled over a section many miles in 

 length, it is highly probable that he will have to record several 

 axes, either anticlinal or synclinal. And it may be that he must 

 notice the occurrence of unstratified rocks along with the stratified. 

 These cannot be represented as occurring in layers, but the nature 

 of their junction with the stratified ones must be carefully noted. 

 Again, the geologist may be at a loss to know certainly how cer- 

 tain formations are disposed beneath the surface, especially upon 

 high land, where the number of ledges are very scanty. Hence 

 he need not fill out the space allotted to him by the altitude, but 

 simply locate in their proper places the respective dips. 



It is necessary often to employ two different scales in protracting 

 sections from notes — one for the horizontal and the other for the 

 perpendicular distances — otherwise the hills will not be conspicu- 

 ous. In the section about to be described, our vertical section is 

 one inch for every one thousand five hundred feet of elevation, and 

 of course for the smaller altitudes proportional parts of an inch. 

 The horizontal section is nearly an inch for every twelve miles. 

 Hence the outline of the surface must be distorted, but this distor- 

 tion will not generally be obvious to the observer. 



The section extends from Mount Desert Island to the Canada 



