Thanks for very useful info, it was just my guess because Covai side had train built first for exporting cotton from the hinterland there to Madras port and could be definitely the oldest line in south. Even in the books I've read there was only info about Goods,fare, earnings and types of goods. Not a passenger service,only fares were written between stations . Mas cstm wasn't connected that early sir, it only started in 1868(2nd ref) . You were right beypore to mas was first, but didn't the route pass through Coimbatore?
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That's why I mentioned 'later on to Raichur and Guntakal'. The link to Bombay was completed in 1871. The construction towards Renigunta from Arakkonam started in 1861 and the line till Cuddapah was complete by 1865. It was paused for a while after that as there was considerable opposition to the route chosen for the Bombay route.
Covai side? Do you mean Coimbatore side?
The south-west line was not built for Madras port. It was mainly built to bring Madras closer to the west. Form...
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the time the Madras railway company was incorporated, their objective was to connect Madras to Beypore (which was considered as the next big place in the South). While this would help in bringing produce and material from the West coast to Madras, more importantly, it would shorten the transit time to Madras by almost 2 days! Ships which earlier, had to go all the way around the southern tip of the continent, could now just dock at Beypore and the cargo, passengers could be sent off to Madras in a little less than a day by train. Further, steamers would move the cargo from Madras to Calcutta.
No, Coimbatore was not on the initial route. The British tried to emulate the American practice of having villages and towns develop around railway stations. Unfortunately, India was already a well-populated country and this did not work. They chose the easiest alignment from Madras to the West Coast, and hoped that the major towns and cities would gradually move towards the line. That's why places like Vellore and Coimbatore are not the main lines. The railway head for Coimbatore was Podanur.
Until 1939, Coimbatore was on the branch line from Podanur to Mettupalayam and passengers had to depend on through coaches connecting trains to go from Podanur to Coimbatore. In 1939, a bypass line was opened at Podanur so that trains going towards MTP (The Niligiri express) need not reverse at Podanur. You can still see this alignment just before Podanur station where the mainline and the line from CBE merge. In 1953, the loop line from Irugur via Coimbatore North was opened that finally brought CBE onto the main route.

Found some relevant info for 1861 & 12-5-1862
1. 1861 TT: 6:15 AM MAS-Tripatoor Train extends CBE in 1862 (shown in 1864 TT: Pic 3)
2. May 1862: proposed inauguration (CBE-PGT 7 AM & CBE-Beypore)
3. 1864 TT: 6:15 AM MAS DEP connects to 7 AM CBE-Beypore (has to wait entire night at CBE). CBE-Beypore extends SA & then MAS (DEP 5 PM)
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1867 TT: All connection remain intact along with 7 PM MAS-CBE New train.
5. 1918 TT: 10 Mail 20:00 PM DEP MAS-MTP. 12 Mail 8:55 AM Dep PDU-MAQ. 5 PM & 7 PM Mail from 1867 TT merged as 10 Mail giving connection to Morning Mail to PDU-MAQ!! 1861 MAS 6:15 AM become passenger. The oldest of the SR Lots!!
Summary: 5 PM CBE-Beypore merged with 7 PM MAS-CBE to become Nilgiri while CBE-PGT extends MAS as Malabar Exp & later Mangalore Exp/Mail!!