ncouratt' in fact so far as the contacts of formations can 

 at ]H't*8cnt be niadi* <»iit, !»nt witli inadi-qnatc detail in show- 

 in«j the changes and variations in the sediments and in the 

 associations of the orjranisms tliey contained. It is not to he 

 infcrretl that snch maps are not of great usefulness. They are 

 the most exact that we have thus far been able to produce and 

 have unquestionably served a useful purpose to those who have 

 had occasion to employ them. 



In the region about Canandaigua lake*, where years of careful 

 study have given us a very detailed knowledge of the changes 

 in sedimentation and tin* variations in the successive faunas, 

 we have undertaken to color the two quadrangles known 

 as the Canandaigua and Xajiles sheets, the former lying directly 

 north of the latter and giving an area which completely encir- 

 cles that lake and affords a rock succession from the horizon 

 of the Salina gypsum beds upward into the basal beds of the 

 Chemung, a vertical thickness of about 3000 feet. During the 

 present season these sheets have been geologically colored, and 

 the detail of the stratigraphy completed with all practicable 

 accuracy; disregarding slight local changes, we have found it 

 possible to represent variations in the sedimentation by a series 

 of 2G colors, where, using the ordinary colors hitherto adopted, 

 one for each (►f the usually recognized formations, nine or 10 

 would have sutliced. Corresponding with this detailed strati- 

 graphic map on which it is planned to register every outcrop 

 of the rocks as well as ajqu-oximately every contact, I have pre- 

 pared a map on the same base showing the succession and varia- 

 tion of faunas, or what may be termed a true paleontologic 

 map. It is i»roposed to issue these maps as companion sheets 

 and to illustrate by means of tlieiu the actual relation of major 

 variations in faunas to variations in sedimentation. In the 

 field work necessary fur the completion of the stratigraphic 

 part of this map. \K 1 ). Lutlnr has supplemented the records 

 made by the paleontologist and himself during the la«t 20 years. 



Areal geology of the Tully quadrangle. Early in the field sea- 

 men it seemed desirable for the purpose of accurate delineation 



