England hopefuls impressive
England hopeful Gary Ballance hit an unbeaten century for Yorkshire against Northamptonshire, while Chris Woakes impressed for Warwickshire.
Ballance finished the opening day at Headingley on 117 not out as the home side reached 328-7 off 92 overs.
Opener Alex Lees fell just 10 runs short of a hundred when he was trapped in front by Andrew Hall, who took 3-72.
Keaton Jennings hit a half-century as champions Durham edged the opening day of their match against Somerset.
The South African opener top scored with 80 with support from Paul Collingwood (36), Gareth Breese (45) and 37 not out from Jamie Harrison as Durham posted 308 all out having been put in at Chester-le-Street.
Lewis Gregory was the pick of the Somerset bowlers with 4-59 as the visitors finished the day on 7-0 after six overs.
Lancashire's decision to bat after winning the toss at Old Trafford proved ill-founded as Warwickshire skittled them out for 247 in the space of 75 overs.
England paceman Chris Woakes did much of the damage with a return of 5-63 off 16 overs with support from Keith Barker, whose 3-52 included openers Paul Horton and Luis Reece with Horton's 83 the major contribution for the batting side.
Varun Chopra and Will Porterfield steered Warwickshire to 63 without loss at stumps.
In Division Two, Will Smith's 70 helped Hampshire reach 231-5 against Derbyshire after England opener Michael Carberry had got them off to a solid start with 45 before falling leg before to Tony Palladino.
Gloucestershire won the toss at Cardiff and put Glamorgan in, but rain limited play to just 19.4 overs.
The home side struggled to 47-6 as David Payne took 3-14 with Will Bragg (25) the only batsman to reach double figures.
There was no play at either Canterbury or the Oval as Kent and Leicestershire and Surrey and Essex were frustrated by the weather.