Ayer was quite a railroad junction at the turn of the century. Many lines crossed and started at or near there, leaving some confusion today. Let me make my attempt to set the record straight.
First off, take a look at the following map from 1917 - it probably presents the clearest image of what went where.
http://historical.maptech.com/getImage. ... g&state=MA
1844 Fitchburg
The first on the scene was the Fitchburg RR. Today, this line is the same route used by the MBTA, running from Boston to Fitchburg.
1846 Worcester and Nashua (Hollis Branch)
Crossing the Fitchburg at grade was the W&N (I incorrectly labled this as the WN&P in my previous post.) This line runs from Worcester through hill yard in Ayer. Today it wyes with the Fitchburg at Ayer. The line north of there is now the Nashua River Rail Trail, running through Groton and Pepperell to Hollis, NH. The line originally went to Nashua and continued onto points northeast.
1847 Peterborough & Shirley (Greenville Branch)
This is the line mentioned in the original post. Starting as a branch of the Fitchburg RR, it left the main line about where the dirt parking lot now is, crossed the W&N (about where the Sovergn Bank is now?) crossed Park Street, and continued behind the Dunkin Donuts.
When the B&M took over all of the above, they changed the layout at Ayer. Eliminating all of the diamonds, the W&N used the P&S grade to get out of Ayer. You can still see evidence of this alignment in the MBTA parking lot. For the P&S, they constructed a new line, which features the bridge over West Main Street, leaving the Fitchburg just West of the tower.
The P&S (commonly referred to as the Greenville branch) remains in service to the 2 industries just north of the 2A crossing. North of there, the rails remain in-place (owned by the MBTA) all the way to Townsend. An attempt to convert the line into a rail trail was killed by the residents of Townsend last year.
For a look of the area after reconfiguration, refer to:
http://historical.maptech.com/getImage. ... g&state=MA
Back to history...
1848 Stony Brook
The Stony Brook was constructed to link the Nashua & Lowell Railroad (at North Chelmsford) to the Fitchburg RR at Ayer. Today these lines join at "Willows", just east of Ayer. However, they were originally constructed as two distinct, parallel lines between Willows and Ayer. This is why the ROW is so wide through that stretch.
1891 Brookline & Pepperell
While it actually left the P&S/Greenville line in Groton at "Squannacook" its close enough to the "Ayeria" to cause confusion. It ran from that point on the P&S/Greenville (a spot in the middle of the woods) to Pepperell, Brookline, and Milford, NH. This is why there are two grades running through Pepperell today: The W&N/Hollis Branch/Bike Path, and the B&P - which has the little classic station just off of Main Street.
I hope this helps someone. For more information, I highly recommend 'The Rail Lines of Southern New England' by Ronald Karr. 90% of my information in this post is from that book. Also, be sure to explore the historical and (relatively) current topo maps at
http://www.maptech.com.
-Ed Lecuyer