iv Report of the Miner alogkal Survey [No. 126.* 



for granted without actual examination, which in this case would have 

 been impossible. 



5. In the Geological Map I have laid down much that has not been 

 actually examined, as might be concluded from what I have stated in 

 my letter to Government, paragraph 7. To refuse to employ those 

 generalisations which the experience of all geologists has shewn to be 

 well-founded, is to forfeit the advantages derivable from the labours of 

 our predecessors, and to impose on ourselves the task of reconstructing 

 the whole science from our own materials. When the same rock has been 

 found on the line of direction in every point in which it has been examined 

 I have deemed myself justified in laying down that rock as continuous 

 through those points. Even at the termination of the survey, many 

 conclusions of this nature must be taken for granted; for it has been 

 well observed, that " no human patience would suffice for the examina- 

 tion of every piece of rock that projects through the surface." And, 

 even were that effected, still much must be taken for granted, especially 

 in these mountains, the rocks being concealed, as they so often are, by 

 deep collections of debris, and covered by luxuriant coats of vegetation. 

 I was, however, in a very early stage of the survey, taught to except 

 from this conclusion granite, as being a rock the occurrence or non- 

 occurrence of which in any particular spot I found I could never pre- 

 dict with any certainty. Limestone also I found seldom could be depend- 

 ed on for any distance, forming always beds in other rocks, and never 

 appearing under those relations which I conceive necessary to constitute 

 a principal [formation. ~\ 



6. The elevations expressed in the sections,* have been determined 

 by barometrical measurement, a method which unless under favorable 

 circumstances, and with great facilities [is liable to error, but] the 

 degree of accuracy attained is sufficient for the purpose, as it is a 

 matter of no importance whatever whether the place of a rock be 

 assigned fifty feet below, or above, its real level. They are as correct I 

 believe as geological sections ever are, and certainly sufficiently correct 

 to answer all the purposes for which they are required. The fixed 

 points determined by the Trigonometrical Survey have been always 



* I regret that the circumstances under which this report has been prepared, have 

 prevented the preparation of these. They are, however, more than half finished, and 

 shall be forwarded with as little delay as possible. 



