234 Note-Taking and the Use of Maps, Etc. — Foerste. 
by any means a new phenomenon, yet it is possible that some 
localities thus published owe their interpretation to indiscrim- 
inate collecting, a fact further aggravated by the common 
practice that the persons who describe the fossils have scarcely 
time to collect- them. For this purpose each locality is usually 
divided into various horizons by lithological characters if the 
same be present and letters are used designating the lines of 
separation, followed by a number indicating the number of 
feet above the same at which a certain specimen was found. 
English capitals are usually used to designate these lines. 
Thus, D, r, 7, G, 38', means that a specimen was found at a 
locality marked 7 on the square of the original map marked 
D, r. A reference to the notes will show that G indicates the 
horizon at the top of the third series of sandstones perhaps at 
some quarry or other, while the appended figure indicates that 
the fossil was collected thirty-eight feet above the same. A 
minus sign ( — ) before the number would indicate that it was 
collected thirty-eight feet before that horizon. 
In glaciated countries where the strata are lithologically 
quite distinct, and are tilted at angles of 45 degrees or more, 
or where there have been eruptions of volcanic material, 
or where a fault has brought dissimilar rocks together 
the structure may have been considerably obscured by the 
drift. In such places the drift itself will very frequently fur- 
nish clews as to the character of at least the general distribu- 
tion of the larger masses of rocks of similar lithological 
features thus hidden. As a rule, admitting many exceptions, 
and which must be studied by practice, it may be stated that 
along an east and west contact line the rock on the south side 
will be apt to appear in the surface drift, or in the fence walls, 
if the surface drift has been disposed of in this way, in angu- 
lar fragments, within at least a few hundred feet from the 
contact line, while the angular bowlders derived from rocks 
found in situ on the northern side of this contact line, appear 
in very much diminished quantity, half a mile south of the 
contact line, and are reduced to about 30 per cent of the angu- 
lar drift three-quarters of a mile south of said contact line, the 
bowlders being often more or less rounded. One mile south 
of the contact line only occasional bowlders are found, often 
quite rounded or diminished in size. Noting the percentage 
of the bowlders of various kinds in the fields and fence walls 
