406 PROCEEDINGS OF THE CALIFORNIA MEETING 



bed of the series here runs from the south about 3 feet high, genei-ally under 

 a sandstone roof, to a locality nearly over the Waldo mine, where it is cut 

 away locally to only a few inches. This instance has been cited as evidence 

 that here is the division between Cretaceous and Tertiary in the region dis- 

 cussed.* It would seem desiral)le, however, that there be found more definite 

 evidence of at least more quantitative importance for designating an oral 

 unconformity than a soft member under a clastic formation deposited appar- 

 ently under locally turbulent conditions. In a country and at a geologic age 

 where so many unusual geologic features — such as have been cited above — 

 are prevalent, only extremely close scrutiny of every obtainable evidence has 

 brought the writer reliable results. 



DEFORMATIOS OF THE COAST liEOlON OF BRIThSn COLUMBIA 



BY CHARLES H. CLAPP 



(Abstract) 



The first period of deformation recorded in the exposed formations of the 

 coast region of British Columbia, by which term is meant that portion of 

 British Columbia which lies to the west of the main crest of the Coast Range, 

 presumably oct-urred at or near the close of the Paleozoic. Although the char- 

 acter and degree of deformation oci-urring at that time has l)een almost en- 

 tirely obscured by later, more intensive deformation and by batholithic intru- 

 .sion. there is some evidence that the folding was of an open character, with 

 the principal axes of folding at a considerable angle to the present prevailing 

 northwest-southeast trend of the rocks of the region. 



The principal period of deformation, as is true of the entire Pacific Coast 

 region, took place near the close of the Juras.sic. This period of deformation 

 can not be dated closely from the known date of the coast region of British 

 Columbia, since the oldest unaffected rocks are of Upper Cretaceous age and 

 rest unconformably on unroofed batholiths intruded during and following the 

 deformation. 



Lower Cretaceous rocks are not found, although they liave been supposed to 

 occur on Queen Charlotte Islands. It was during this period of deformation 

 that most of the rocks of the region attained their general northwest-southeast 

 trend. The folding occurred in the zone of combined fracture and flow, so the 

 weaker rocks were deformed to closed folds of the similar type, while the 

 more competent rocks were deformed into parallel folds of a more open char- 

 acter. Batholithic intrusion took place during this deformation, producing 

 primary gneisses, although later batholiths appear to have been intruded after 

 most, if not all, dynamic movement had ceased. 



Portions of the coast i-egion were profoinidly affected by the next period of 

 deformation, which does not appear to have taken place luitil the close of the 

 Eocene. The rocks were warped into rather broad folds, whose general north- 

 east-southwest axes were determined by the l)uttresses of older and more com- 

 petent rocks. Extensive faulting, also, largely of a reversed or overthrust 

 character, took place at this time and in places stocks of subjacent rocks were 

 inti'uded. 



U. S. Geological Survey Bull. 531.1, l'Ji:5, p. lo. 



