Trains were cancelled from Aberdeen to Edinburgh and Glasgow on Thursday after a safety issue forced a total closure of the railway line through Angus.
Services were unable to run for two hours after part of the surface beneath the tracks slipped away between Arbroath and Montrose stations.
The defect, which affected the line just north of Arbroath, was reported at about 11.20am.
Some of the stone ballast beneath the line is said to have led to a small dip, making it less steady.
A safety inspection was carried out and engineers quickly firmed up the track-bed.
The line reopened at 1.20pm, however cancellations, delays and revisions to services from Aberdeen to Edinburgh and Glasgow continued into the evening.
The 17.06pm Glenrothes to Edinburgh, 5.09pm Arbroath to Edinburgh, 8.57pm Aberdeen to Inverurie and the 9.25pm Inverurie to Aberdeen services were among those cancelled with ScotRail citing “a safety inspection of the track” as the reason.
A Network Rail spokesman said: “Our engineers were on-site quickly to repair the track and reopen the line for passengers.
“We understand the inconvenience this incident will have caused to some customers, but a short closure of the line was unavoidable as any track defect must be quickly inspected to ensure the line is safe for trains to use.”
ScotRail posted: “Following a safety inspection on a train earlier today between Arbroath and Montrose the line is now open. Disruption is expected until 3pm.
“Train services between Aberdeen and Edinburgh are returning to normal but some services will still be cancelled, delayed or revised.”
UPDATE: Although services are returning to normal, we've got a maximum speed in place of 50 mph. Please check your journey online for updates here ?https://t.co/J1m2DnhAEG ^Carrie
— ScotRail (@ScotRail) September 12, 2019
Earlier the firm tweeted: “We have had reports of a suspected track defect between Arbroath and Montrose, for safety reasons services will be unable to run between these stations.”